1. happening or existing without the knowledge of someone specified —usually used with to <unbeknownst to us rumors were flying> (Merriam-Webster Online).
2. a word that pretentious pricks use to try to sound smarter than they actually are.
Not a word pretentious pricks use. An extremely highly intellijated.., (also a new one) word, that only people with common fuckin' sense do. Actually, the proper spelling includes an apostrophe prior to the T.