Hypothesis
Part of speech: noun
Definition: A tentative conjecture explaining an observation, phenomenon or scientific problem that can be tested by further observation, investigation and/or experimentation. (general) An assumption taken to be true for the purpose of argument or investigation. The antecedent of a conditional statement.
Example sentence: The shrewd guess, the fertile hypothesis, the courageous leap to a tentative conclusion - these are the most valuable coins of the thinker at work. But in most schools guessing is heavily penalized and is associated somehow with laziness.
Supposition
Part of speech: noun
Definition: Something that is supposed; an assumption, conjecture or speculationThe act or an instance of supposing