vocabulary - Word that describes a word which isn't normally used in an everyday conversation

I remember there was a word which describes a word which isn't normally used in an everyday conversation. Ironically, that word isn't normally used in an everyday conversation.

It's an adjective. In a sentence:

That word is ??????, you don't see it often.

I can distinctly remember that it is used to specifically describe words (and not general events, knowledge etc). A word which is rare/exquisite and isn't seen very often.

What is a word that describes that? I remember it was quite the highbrow word.