hypothesis

n. (pl. -theses) proposition or supposition made as the basis for reasoning or investigation. [greek, = foundation]

n. A supposition; a proposition or principle which is supposed or taken for granted, in order to draw a conclusion or inference for proof of the point in question; something not proved, but assumed for the purpose of argument, or to account for a fact or an occurrence; as, the hypothesis that head winds detain an overdue steamer.