flexible (adj.)youdaoicibaDictYouDict[flexible 词源字典]
early 15c., "capable of being bent; mentally or spiritually pliant," from Middle French flexible or directly from Latin flexibilis "that may be bent, pliant, flexible, yielding;" figuratively "tractable, inconstant," from flex-, past participle stem of flectere "to bend," which is of uncertain origin. Flexile (1630s) and flexive (1620s) have become rare. Related: Flexibly. Coles' dictionary (1717) has flexiloquent "speaking words of doubtful or double meaning."[flexible etymology, flexible origin, 英语词源]