circumflex (n.)

"sign or mark placed over certain vowels to indicate accent or tone," 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 the shape. The tone is recognized in Latin, Greek, and Sanskrit; in the first two it is limited to "long" vowels. "In modern English use the mark has no definite value, but is variously used by orthoepists or phonetists to mark long quantity, 'broad' quality, or the like" [OED].