— unthinkability, unthinkableness , n. — unthinkably , adv.
/un thing"keuh beuhl/ , adj.
1. inconceivable; unimaginable: the unthinkable size of the universe.
2. not to be considered; out of the question: Such a suggestion is unthinkable.
n.
3. something that cannot be conceived or imagined, as something too unusual, vague, or disagreeable: Today's unthinkables are tomorrow's realities.
[ 1400-50; late ME; see UN- 1 , THINKABLE ]