Yours, Etc.: Origins and Uses of 8 Sign-Offs
1832, first used of a 15c.-16c. architectural style with flame-like curves, from French flamboyant "flaming, wavy," present participle of flamboyer "to flame," from Old French flamboier (12c.), from flambe "flame," from flamble, variant of flamme, from Latin flammula (see flame (n.)). Extended sense of "showy, ornate" is 1879. Related: Flamboyantly.