An assumption taken to be true for the purpose of argument or investigation.
Used loosely, a tentative conjecture explaining an observation, phenomenon or scientific problem that can be tested by further observation, investigation and/or experimentation. As a scientific term of art, see the attached quotation. Compare to theory, and quotation given there.
The antecedent of a conditional statement.
Something supposed; a supposition, a hypothesis.
The act of supposing; supposition.