amaranth (n.)

1610s, from French amarante, from Latin amarantus/amaranthus, from Greek amarantos, name of a mythical unfading flower, literally "unfading, undecaying," from a- "not" (see a- (3)) + stem of marainein "die away, waste away, decay, wither; quench, extinguish," from PIE root *mer- "to rub away, harm" (also "to die" and forming words referring to death and to beings subject to death). In classical use, a poet's word for an imaginary flower that never fades. It was applied to a genus of ornamental plants 1550s. Ending influenced by plant names with Greek -anthos "flower."