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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.
Unbeknownst to you, I have been fucking your sister for the past six months.

My dad has been sick for years, unbeknownst to the family.
by TCAcycle February 05, 2010
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