Open English Wordnet
Nouns
(n)hypothesis, possibility, theorya tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena“a scientific hypothesis that survives experimental testing becomes a scientific theory”, “he proposed a fresh theory of alkalis that later was accepted in chemical practices”
(n)guess, conjecture, supposition, surmise, surmisal, speculation, hypothesisa message expressing an opinion based on incomplete evidence