adj. - a woman that in no conceivable way would have sex with the other parties at hand. Out of his league, untouchable or "only in your dreams". Only used when no one present has any realistic and/or legal means of penetrating the pussy of the subject, direct object or indirect object which the adjective refers to. (In a grammatical sense; this does not imply that women are subjects or objects.) May also refer to a hook up that no one believes and is totally unverifiable.
Other spellings: impussable, impussible, im-fucking-pussyble.
Jessica Alba is impussyble!
A: Dude I hooked up with that cheerleader after our World of Warcraft session last night.