infrequency (n.)youdaoicibaDictYouDict[infrequency 词源字典]
c. 1600, from Latin infrequentia "a small number, thinness, scantiness," noun of quality from infrequentem (see infrequent). Related: Infrequence (1640s).[infrequency etymology, infrequency origin, 英语词源]