"speculation, an unproven assumption, a belief, policy, or procedure proposed or followed as the basis of action," and "conjecture."
What Webster's (online) dictionary has to say about the word theory:
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1. 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".
2. A tentative theory about 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".
3. 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".
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Webster's then goes on to explain that Definition #1 is the definition used in scientific literature.
And so long as the willfully ignorant cling to the fanciful notion that dictionary definitions are like some sort of egalitarian etymological smorgasbord, where they get to pick and choose which definition they want to interchangeably apply, and when, there is no hope of counteracting their ignorance and mendacity.