Is it legal to attempt to redefine legal terms?

Question

If a term or phrase has a specific (and relevant) legal definition in UK law, can I use it to mean something else, and can I use it to mean something else without first telling the other party what I mean instead? (to be clear; I'm not actually trying to do this, but someone else is trying to do it to me).

For example: In the UK, the definition of a Licensed Premises is set out in The Licensing Act 2003 as [a] premises in respect of which a premises licence has effect.

Given this, can I legally use the phrase 'licensed premises' to refer to only those parts of the premises that I intend to sell alcohol from, rather than the entire premises?

I see three possible options:

1. I can use the phrase to mean whatever I like, the fact that a legal term with the same phrasing exists is irrelevant
2. I can use the phrase, but only if I make it clear that I am redefining it. If I don't redefine it, then it has it's normal legal meaning.
3. I cannot redefine the phrase at all. It has it's normal legal meaning, and only Parliament can make it mean something else

My gut feeling is that 2) is broadly correct, as the other two seem like they would lead to issues, but I suspect that the answer is (as always) more complicated than that.

Answer 1

This would only arise in a contractual context. In litigating a breach, idiosyncratic private beliefs of the parties would not matter, what matters is what was objectively agreed on. So words are interpreted as having their ordinary meaning, unless there is a special stipulation as to the meaning of a term in the contract. There may be some dispute over what the "ordinary meaning" is, which may be resolved by introducing testimony from language experts or by looking at surrounding circumstances.

The "ordinary meaning" of a word or phrase is often so broad with respect to the intended agreement that a narrowing of the definition is necessary (or sometime the definition is expanded). Words are not wholly redefined (redefining "house" to mean "cat"). Many things can be deemed to be "private use", and it may be desirable to specifically say that it means "exclusive use by the party of the first part". Unless you overtly signal a change in scope of the term, you inherit all of the problems of ambiguity attached to the plain meaning of the term (in some contracts, that specifically works in favor of the other party).

If you are not talking about a contract, then you are socially free to to use "glory" to mean "a nice knock-down argument", at your social peril. If you are talking about what you are to do in light of some government requirement e.g. to pay taxes, it does not matter if you attach a note saying that you define "income" to mean "money that falls from the sky", income is whatever the government defines it as, even if you are ignorant of or don't agree with that definition. Governmental word definitions pertain to particular Acts. If the term "wealth" is defined in a specific way in some act, that does not mean that the term always is assigned that meaning everywhere. However, if the government has defined a term in some context, there is a reasonable chance that in that context a contract will be interpreted following that definition. This is because all parties are assumed to know the law and therefore know that "licensed premise" has a particular meaning with respect to liquor sales. A contract could explicitly override that definition, but without such a clause, the statutory definition is evidence of what the objective meaning of the term is taken to be.