WordWeight : Weighing the Words

Pronunciation : Sup`po*si"tion
Part of Speech : n.
Etymology : [F. supposition, L. suppositio a placing under, a substitution, fr. supponere, suppositium, to put under, to substitute. The word has the meaning corresponding to suppose. See Sub-, and Position.]
Definition : 1. The act of supposing, laying down, imagining, or considering as true or existing, what is known not to be true, or what is not proved.

2. That which is supposed; hypothesis; conjecture; surmise; opinion or belief without sufficient evidence. This is only an infallibility upon supposition that if a thing be true, it is imposible to be false. Tillotson. He means are in supposition. Shak.
Source : Webster's Unabridged Dictionary, 1913