1570s, from Latin (accentus) circumflexus, "bent around," past participle of circumflectere "to bend around," of a charioteer, "turn around" (from circum "around;" see circum-, + flectere "to bend;" see flexible); used as a loan-translation of Greek (prosodia) perispomenos (Dionysius of Halicarnassus), literally "drawn-around," with reference to shape.
