You don’t need to know who Amy Winehouse is to be a good judge. But members of the judiciary worried about bad press if they don’t get a reference to her, or if they have to ask “what are arctic monkeys?” can now take comfort from a new online dictionary resource. The latest Collins English Dictionary includes, in its online bibliographical section, an entry on various contemporary figures. The dictionary also includes new words like “hoodie” and “leetspeak” (jargon used by internet groups).

Dictionaries are law books in disguise. They contain answers to over 100,000 legal questions. The reason is that laws are made in words, and, quite commonly, you can’t tell exactly what a law means until a court has ruled whether the words in it apply to a given situation. Laws contain thousands of words that, depending on how they’re defined, might bankrupt someone, allow someone else to win a fortune, determine a child’s residence, keep someone in prison for life, save the life of an animal in zoo, permit an abortion, or put a multimillion pound bill on the desk of a local authority.

Dictionaries don’t themselves automatically determine the meaning of a word but they’re often used by courts as a useful and authoritative starting place. As the American judge Justice Learned Hand warned in 1935, we shouldn’t “make a fortress out of the dictionary”. Dictionaries, though, are useful guides that need to be consulted by courts to give language some consistency - we wouldn’t want to live under a system where the Humpty Dumpty’s rules applied. In Lewis Carol’s book Through The Looking Glass, in a dispute between Alice and Humpty Dumpty about the word “glory”, Humpty says “When I use a word it means just what I choose it to mean – neither more nor less”.

Hundreds of major cases have been judged with the assistance of entries in the dictionary. The human drama involved in these cases is diverse and is reflected in the range of words for which courts have sought dictionary definitions. In recent cases, dictionaries have been used to get authoritative definitions of many words including: curtilage (a small piece of ground attached to a dwelling house), debris, fungicide, logo, trivial, well known, crane, leaflet, bootleg, caravan, to influence, sick, audit, and nerd.

In a case from 1994, a court upheld the conviction of Eric McFarlane for living off the earnings of prostitution. He had argued that as the income in question, from his partner Miss Josephs, came to her in her work as a “clipper”, there was no prostitution involved. A clipper is someone who offers sexual favours for reward but who takes the money without intending to provide the favours. She took up to £400 a night in central London doing this. After consulting precedents and dictionary definitions the court decided that the crucial feature defining prostitution was “the making of an offer of sexual services for reward”. That included what a clipper did, so Mr McFarlane was guilty of living off such earnings.

Even where a dictionary is consulted but provides no answer, that in itself can help to conclude a dispute. In 2003, in a case about rap music, one artist claimed damages because he said that his song had been subject to “derogatory treatment” by another artist. Mr Justice Lewison had to discern the meaning of phrases like “mish mash man” and “shizzle my nizzle”. Andrew Alcee, the writer of Burnin, a track that was a hit for Ant’ill Mob, claimed that lyrics "laid over" the top of the Heartless Crew's remix of the song constituted derogatory treatment of the copyright. Mr Alcee claimed that terms like "shizzle my nizzle", "mish mish man" and "string dem up" referred to drugs and violence and so "distorted and mutilated" his original tune. The judge said (referring to himself and the barristers) that the claim had led to the "faintly surreal experience of three gentlemen in horsehair wigs examining the meaning of such phrases". He admitted that even after playing the record at half speed and referral to the Urban Dictionary on the internet he was unable to be sure of the meaning of the slang. He concluded that the latter words “for practical purposes were a foreign language”. The action for damages failed.

In most cases where courts have to interpret the meaning of an ambiguous word, a great deal of reading, thinking, and analysis must be done by the judges. Law can’t be done successfully by googling “define:” for a word, and pressing Enter. After all, the only place where success precedes work is the dictionary.

Professor Gary Slapper is Director of the Centre for Law at The Open University

Times Recommends

• The best legal yarns this Christmas
• Legal school 'earned £1m by exploiting bar course'
• Axe may fall on 5,000 more City lawyers