disloyal (adj.)youdaoicibaDictYouDict[disloyal 词源字典]
early 15c. (implied in disloyally), from Old French desloial, desleal (Modern French déloyal) "treacherous, false, deceitful," from des- (see dis-) + loial (see loyal).[disloyal etymology, disloyal origin, 英语词源]