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"
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"
a state of extreme (usually irremediable) ruin and misfortune; "lack of funds has resulted in a catastrophe for our school system"; "his policies were a disaster"