- inconceivable; unimaginable: the unthinkable size of the universe.
- not to be considered; out of the question: Such a suggestion is unthinkable.
- something that cannot be conceived or imagined, as something too unusual, vague, or disagreeable: Today’s unthinkables are tomorrow’s realities.
- not to be contemplated; out of the question
- unimaginable; inconceivable
- unreasonable; improbable
adj.early 15c., “too large to be conceived, unimaginable,” from un- (1) “not” + thinkable (see think). Meaning “incapable of being framed by thought” is recorded from mid-15c.