1. A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation.
2. Something taken to be true for the purpose of argument or investigation; an assumption.
3. The antecedent of a conditional statement.

[Latin, subject for a speech, from Greek hupothesis, proposal, supposition, from hupotithenai, hupothe-, to suppose : hupo-, hypo- + tithenai, to place.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.