Noun

• S: (n) theory (a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena) "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory"
• S: (n) hypothesis, possibility, theory (a 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"
• S: (n) theory (a belief that can guide behavior) "the architect has a theory that more is less"; "they killed him on the theory that dead men tell no tales"