Merriam-Webster's Collegiate® Dictionary, 11th Edition
OBVERSE
I. adjective see: ob-
Date: circa 1656
facing the observer or opponent, having the base narrower than the top , constituting the obverse of something ; opposite , obversely adverb
II. noun
Date: 1658
the side of a coin or currency note bearing the chief device and lettering, a counterpart having the opposite orientation or force , a proposition inferred immediately from another by denying the opposite of what the given proposition affirms