Americans (and people of several other cultures) are generally plagued with the notion that not knowing a word that a colleague uses is cause for embarrassment or even shame, as it implies a lack of education. In order to accommodate our fellows, we have taken to using a small vocabulary in order to not embarrass our fellows.
But not knowing a word is not an embarrassment; it is an opportunity to learn! We should enthusiastically embrace the chance to expand our lexicon – and, as a result, our ability to express ourselves. Our friends would hardly disown us for asking a question to further our own education. In fact, learning is among the choicest benefits of friendship.
On the other hand, it is an embarrassment to be a mumpsimus.