untruth (n.)youdaoicibaDictYouDict[untruth 词源字典]
Old English untreowþ "unfaithfulness, treachery," from un- (1) "not" + truth (n.). Similar formation in Old Norse utrygð. Meaning "falsehood" is attested from mid-15c., as is that of "a lie." Related: Untruthful.[untruth etymology, untruth origin, 英语词源]