TibyoudaoicibaDictYouDict[Tib 词源字典]
1530s, typical name for an English woman of the lower class, hence "girl, lass, sweetheart," sometimes also "strumpet," from the pet form of Isabel. Often paired with Tom, as Jill was with Jack. Colloquial St. Tibb's Eve (1785) was the evening of the last day, the Day of Judgement, hence "never."[Tib etymology, Tib origin, 英语词源]