inconstant (adj.)youdaoicibaDictYouDict[inconstant 词源字典]
c. 1400, "fickle, not steadfast," from Middle French inconstant (late 14c.), from Latin inconstantem (nominative inconstans) "changeable, fickle, capricious," from in- "not, opposite of, without" (see in- (1)) + constantem (see constant). Related: Inconstantly.[inconstant etymology, inconstant origin, 英语词源]