Linguistics term for word choice

I was taught a word once by a linguist. I can't remember it, but it would be very useful for a Google search I am trying to do to solve another question on a different StackExchange.

It was a similar word to vocabulary, but rather than refer to all the words a person knew, it referred to the set of words a person would choose to use in a particular situation. English speakers from different regions might select different words from the set of swimmers, trunks, cossies, bathers, while understanding they are all referring to the same thing - they are all in their vocabularies, but not in their [blank].

My recollection was the linguistics term was also a common English word, like class or style, which made it confusing when I first encountered it.

Solution 1:

I have found the word I was looking for.

In linguistics, a register is a variety of a language used for a particular purpose or in a particular social setting.

In hindsight, the definition I gave was roughly right, but the swimmers example seems to have been inappropriate and hence distracting. Sorry.

Solution 2:

Not a standard technical distinction, but if I saw vocabulary and repertoire in the same sentence, I'd assume vocabulary is those words & meanings someone is capable of understanding, where repertoire means only those the person actually uses.

If OP will accept a two-word term, the most suitable is probably active vocabulary (as opposed to passive, being words understood but not used).

There is also productive vocabulary (normally contrasted with receptive), but I don't like that because "productive" in linguistics usually applies to a word or term to means it's often used to make new words or terms, or has its meaning easily stretched into to new areas.

This NGram shows active vocabulary is consistently used more than productive vocabulary.

Solution 3:

Productive Vocabulary

The body of words that a person feels comfortable using in writing and speech. Similar to expressive vocabulary. A person's productive vocabulary is usually smaller than their receptive or listening vocabulary.

education.com

Solution 4:

I know this answer is years later but what about the word "lexicon" as the answer to your question? Lexicon