early 15c., reflexive, "conduct or comport" (oneself, in a specified manner), from be- intensive prefix + have in sense of "to have or bear (oneself) in a particular way, comport" (compare German sich behaben, French se porter). Cognate Old English compound behabban meant "to contain," and alternatively the modern sense of behave might have evolved from behabban via a notion of "self-restraint." In early modern English it also could be transitive, "to govern, manage, conduct." Related: Behaved; behaving.
