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 vocabularyvocabulary, 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"swimmers, "cossies"trunks, "bathers"cossies, etc.bathers, while 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 linguistic jargon wordlinguistics term was also a common English word, like "class"class or "style"style, which made it confusing when I first encountered it.