\Hy*poth"e*sis\, n.; pl. {Hypotheses}. [NL., fr. Gr.
? foundation, supposition, fr. ? to place under, ? under + ?
to put. See {Hypo-}, {Thesis}.]
1. 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.
         An hypothesis being a mere supposition, there are no
         other limits to hypotheses than those of the human
         imagination.                          --J. S. Mill.
2. (Natural Science) A tentative theory or supposition
   provisionally adopted to explain certain facts, and to
   guide in the investigation of others; hence, frequently
   called a working hypothesis.
Syn: Supposition; assumption. See {Theory}.
{Nebular hypothesis}. See under {Nebular}.