Over time, much of Shakespeare's colourful language has been lost to the editor's pen. In the RSC's new edition of his works, H¨¦lo?se S¨¦n¨¦chal and Jonathan Bate have rediscovered some of the original 'linguistic exuberance'

Possessed of a vocabulary of at least 20,000 words, Shakespeare was the man who gave us terms such as "hunchbacked", "tranquil", "schoolboy", "coldhearted" and "shooting star". It was Shakespeare who gave the owl his cry of "tu-whit, tu-woo" (although "whit" and "woo" are in fact individual mating calls made by separate owls). He invented now familiar phrases such as "skimmed milk" and "dead as a doornail", and maxims such as "the course of true love never did run smooth". He relished the very sounds of words - the belched belligerence of "garboil", the scrambled incoherence of "skimble-skamble" and the hissed fastidiousness of "prenzie".

In his plays, he refers to "words" more than 800 times, to "speaking" over a thousand, and his characters don't just "speak" - they "howl", "carp", "buzz", "lisp", "rant", "mutter" and "drawl". Like the theatre for which he wrote, Shakespeare's plays are shifting seas of words and sound, from the "sweet airs" and narcotic "voices" that haunt a magical island to the lively "brabble" of drinkers at a London tavern and the sound and fury of the "dogs of war". He even incorporated the notoriously noisy playhouse audience into his soundscape: in The Tempest they double up as the sea, surging round the three sides of the stage as it becomes the deck of a storm-tossed boat. Shakespeare calls them "roarers", a word that neatly encapsulates two senses of "noisy waves/riotous revellers".

One of the challenges in working on the Royal Shakespeare Company's new edition of Shakespeare's works has been how to return this sense of linguistic exuberance to the text. In a highly literate age such as ours, we need to remind ourselves that in 1600 language was not primarily writing, but speech and sound. Spelling was not standardised, and monolingual dictionaries did not exist. Languages themselves were known as "tongues".

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When Shakespeare wrote "mettle", it is not always clear whether he meant "spirit, temperament" or "metal". Frequently, of course, both meanings are present. When Macbeth tells his wife that, should she have children, her "undaunted mettle should compose/ Nothing but males" he plays on the idea that, as a "metal", she should be used to make "mails" (chainmail armour).

Meaning existed, as Shakespeare's Sonnet 81 has it, "where breath most breathes, ev'n in the mouths of men". His sense that words were alive is neatly demonstrated here by the fact that the reader must pause to breathe after the comma in the middle of the line.

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His plays are packed with puns: sole/soul, eye/I, horse/whores/hoars/hares. Some of these need a note on contemporary pronunciation. Falstaff's "Give you a reason? If reasons were as plenty as blackberries, I would give no man a reason" is tricky if we do not know that "reason" was pronounced "raisin". Others are more straightforward: the soldier Pistol's blustering threat to "firk" ("beat") a captured Frenchman has the unfortunate result of being heard as an altogether more explicit proposal. The French princess Katherine who is to marry Pistol's king similarly misunderstands "foot" as " foutre " ("fuck" in French).

The mangling and malapropisms of foreigners, of bumbling police constables and affected courtiers demonstrates the endless slipperiness of Elizabethan English, a language in which the meanings of words were not fixed and Shakespeare did not reside silently in the pages of a book.

In the foreword to the new edition, Michael Boyd calls the Shakespearean text a "blueprint for performance to a live audience", its words rippling with a host of possible linguistic and theatrical senses that it is important for the on-page notes to provide access to.

A Midsummer Night's Dream , for example, features a play in which a character represents a wall with a hole in it, through which two lovers whisper and try to kiss. "My cherry lips," moans the lovelorn Thisbe, "have often kissed thy stones,/ Thy stones with lime and hair knit up in thee."

Traditionally, the actor playing the wall arrives on stage wearing a brickwork-patterned board or sheet, extending his fingers in an "O" to represent the chink the lovers peer through. But the language reveals that there is a different - and funnier - joke here altogether. The word "stones" can also mean "testicles", "lime" was pronounced "limb" (a word for a penis) and "hair" probably needs no explanation.

Our discoveries of wicked new theatricality in the language have already filtered into RSC productions such as Gregory Doran's Dream , in which, The Guardian reviewer said, "the real success (was) pulling off an exceptionally funny play within a play".

Annotating the Shakespearean text should be a means of opening up these double-hinged doors of language. In the RSC edition, we have tried to generate a sense not only of the sounds of words but of the "non-standard" meanings that often accompanied the primary senses of words. Shakespeare's sexual language and slang fell victim to the great editorial tradition of the 18th century, an age of dictionary-making possessed by a desire to fix language and regularise spelling.

In his famous Dictionary , Dr Johnson sought to "secure our language from being overrun with cant... crowded with low terms", to "facilitate", "settle" and "civilise" English. A number of Shakespeare's colloquial references simply evaded editors. Many of them, however, were deliberately purged and pruned, dropped from the explanatory notes, inaccurately defined or only partially glossed. Mercutio's song about syphilis in Romeo and Juliet was dismissed by one editor as "a not very intelligible fragment of some ballad", for example.

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Shakespeare's energetic engagement with the vagaries and vulgarities of everyday speech was incompatible with his emerging status as a national icon. When editing "divine Shakespeare", a 18th-century scholar declared, one was responsible for "restoring to the Publick their greatest Poet in his original Purity". Until very recently, there has been a continued reverence for the Bard that often leads to all sorts of words being dismissed, unhelpfully, as "bawdy quibbles", "obscure" or "of uncertain meaning". Even the Oxford English Dictionary does not cater for all meanings that were active in the 16th century.

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In preparing the RSC edition, we have been able to take advantage of electronic resources that are revolutionising the way we understand Shakespeare's language. When it comes to getting a clearer idea of spoken or informal English, being able to search digitised databases of ballads, proverbs and letters is invaluable. Vast collections of poetry, prose and drama are now available online and can be searched quickly and accurately.

This gives us a sense of how words were operating in a huge variety of contexts; it has enabled us to see that, while Shakespeare certainly invented a considerable number of words, many of the terms the OED identifies as Shakespearean coinages had been used by others before him. Similarly, words that the OED gives a later date to are shown to have been alive and well in the 16th century.

Searching the growing number of online texts, and employing the recent specialist dictionaries they have helped to create, tells us that Troilus' instruction to "wear a castle on thy head" refers to a type of helmet, and that the French Dauphin's boast that he has besieged or "banked" enemy towns is a card-playing metaphor referring to securing one's winnings. Tom Snout, the tinker in A Midsummer Night's Dream , is thought to have been named after the spout of a kettle, but 16th-century kettles did not have long nozzles; instead, texts from the period show that "snout" could refer to the lip of a lidded drinking vessel. Perhaps this is a character who, in addition to possessing a large (or red) nose ("snout"), is fond not only of mending but of drinking from pewter tankards. A search of contemporary drinking songs throws up a number of inebriated "Tom Tinkers".

Many of the new resonances to emerge in the preparation of this edition relate to technical language - legal or medical terminology for example. Lady Macbeth's "a little water clears us of this deed" refers both to cleansing the hands of blood and to being exonerated of a criminal act. When Romeo makes "a dateless bargain to engrossing death", death is seen as both all-consuming and as an exacting lawyer who has "engrossed" (copied out in legal hand) the contract on Romeo's life.

In Hamlet , images of disease and medicine feature prominently. During the play-within-a-play he has staged to catch out his murderous uncle, Hamlet mutters: "Wormwood, wormwood." The herb is bitter tasting and is usually glossed as a comment on how hard it is for Claudius to witness his violent actions being re-enacted before him. But Elizabethan herbals and medical texts also tell us that "wormwood... killeth the worms in the belly". The play thus becomes the means of provoking forth the gnawing worm of Claudius' conscience. Interestingly, one of the means of taking the cure was in a preparation dropped into the ears, the orifice through which Claudius poisons his brother. Hamlet may additionally be thinking of Claudius as a doomed rat; household advice books tell us that wormwood was used to draw out rodents from among the rushes on the floor.

Hamlet contains a particularly large number of herbal references; it may or may not be relevant that the herbs that a distraught and unstable Ophelia hands out are all abortifacients. Such connotations may be more pertinent to Biondello's glib tale, in The Taming of the Shrew , of "a wench married in an afternoon as she went to the garden for parsley to stuff a rabbit (strumpet)".

Electronic resources do not only unveil new meanings or interesting contextual information; they also give a striking sense of the fluidity of 16th-century English. Although monolingual dictionaries did not exist, there were many bilingual and trilingual guides to Latin, French, Italian and Spanish, all of which are now available in digitised form. We can gain a sense of the meanings of English words by looking at how they function to define a foreign word. "Foul", for example, is listed in various dictionaries as synonymous with "unclean, loathsome, full of dregs, nasty, base, ill-favoured, niggardly, pitiful, shameful, infamous". It appears as a descriptor of excrement, illegible handwriting, bad weather, poor morals, infected ulcers.

The vast majority of Shakespeare's words contain a spectrum of related yet distinct meanings, which editors ignore at their cost. When Macbeth imagines life as "a walking shadow, a poor player" - the words "walking shadow" vibrate with the simultaneous senses of "haunting ghost", "strutting actor", "living portrait", "fleeting ephemera". It has been a priority of the RSC edition to try to restore some of this delicious multiplicity to the text; our notes endeavour to flag up not only actively different meanings generated by a word or phrase but to demonstrate the way related senses shade into one another.

Excitingly, we are continuing to discover new meanings for Shakespeare words every day. Language was a precious treasury to the playwright; he calls it an "exchequer" in which a "mint of phrases" constantly coined forth "fire-new words". More of a shape-shifter than the actors themselves, the "gentle spirit of moving words" that inhabits the plays has the power to "move" us profoundly, even as its essence shifts restlessly onwards.

H¨¦lo?se S¨¦n¨¦chal is chief associate editor of the RSC Shakespeare. Jonathan Bate is professor of Shakespeare and Renaissance literature, department of English and comparative literary studies, Warwick University.

The RSC Shakespeare: The Complete Works , edited by Jonathan Bate and Eric Rasmussen, is published by Palgrave Macmillan, ?30.00.

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