Well I really know every word I say, or at least I think I do, so I may have done that but I don't think so. I try not to use words I don't really know just in case someone does.
I do that astutely.
it's called contextualizing. it happens most when reading or listening: you intuitively learn the meaning of a word by the words around it without actually knowing precisely what the word means. it can backfire though.
I guess I do get lucky sometimes!