Is it ensure, insure, or assure?
1610s, from French amarante, from Latin amarantus, from Greek amarantos, name of an unfading flower, literally "everlasting," from a- "not" + stem of marainein "die away, waste away, quench, extinguish," from PIE *mer- "to rub away, harm" (see nightmare). 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."