being of crucial importance; "a pivotal event"; "Its pivotal location has also exposed it to periodic invasions"- Henry Kissinger; "the polar events of this study"; "a polar principal"
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"
a proposal intended to explain certain facts or observations