Definition of: hypothesis

(hī·poth′ə·sis, hi-) noun plural ·ses (-sēz)
1. A set of assumptions provisionally accepted as a basis of reasoning, experiment, or investigation.
2. An unsupported or ill-supported theory. [<NL <Gk., foundation, supposition <hypotithenai put under <hypo-under + tithenai put] Synonyms: conjecture, guess, scheme, speculation, supposition, surmise, system, theory. A hypothesis is a statement of what is deemed possibly true, assumed and reasoned upon as if certainly true, with a view of reaching truth not yet surely known; especially, in the sciences, a hypothesis is a comprehensive tentative explanation of certain phenomena, which is meant to include all other facts of the same class, and which is assumed as true till there has been opportunity to bring all related facts into comparison; if the hypothesis explains all the facts, it is regarded as verified; till then it is regarded as a working hypothesis, that is, one that may answer for present practical purposes. A hypothesis may be termed a comprehensive guess. Compare GUESS, SYSTEM, THEORY. Antonyms: certainty, demonstration, discovery, evidence, fact, proof.