Definition of: supposition

(sup′ə·zish′ən) noun
1. The act of supposing, or that which is supposed; conjecture.
2. A hypothetical proposition made for the purpose of explaining certain facts, relating them, or of deducing consequences from them; hypothesis. See synonyms under FANCY, GUESS, HYPOTHESIS, IDEA, THOUGHT. [<Med. L suppositio, -onis <L, a substitute <suppositus, pp. of supponere suppose, substitute <sub- under + ponere place]
—sup′po·si′tion·al adjective
—sup′po·si′tion·al·ly adverb