INCONCEIVABLE
impossible, inconceivable, out of the question, unimaginable
(adjective) totally unlikely
Source: WordNet® 3.1
Etymology
Adjective
inconceivable (comparative more inconceivable, superlative most inconceivable)
Unable to be conceived or imagined; unbelievable.
Antonyms
• conceivable
Source: Wiktionary
In`con*ceiv"a*ble, a. Etym: [Pref. in- not + conceivable: cf. F.
inconcevable.]
Definition: Not conceivable; incapable of being conceived by the mind; not
explicable by the human intellect, or by any known principles or
agencies; incomprehensible; as, it is inconceivable to us how the
will acts in producing muscular motion.
It is inconceivable to me that a spiritual substance should represent
an extended figure. Locke.
– In`con*ceiv"a*ble*ness, n.
– In`con*ceiv"a*bly, adv.
The inconceivableness of a quality existing without any subject to
possess it. A. Tucker.
Source: Webster’s Unabridged Dictionary 1913 Edition