Tib and Tibb originated in the 13th century as nicknames for Theobald (for boys) and Isabel and Isabella (for girls). As Isabel grew in popularity, Tib(b) was used more often on girls. By the 16th century, Tib was a term for a young girl, much like Tom was for young boys. A form of Elizabeth, Tib seems to have developed in Provence. A popular English name in the Middle Ages; pet forms included Ibb, Libbe, Nibb, Tibb, Bibby. (Source: google)