As a medieval given name this is a Norman form of the French name Thierry, from Germanic Theodoric, from þeud ‘people, race’ + rīc ‘power, ruler’. This was adopted by the Normans and introduced by them to Britain. In modern English use it seems at first to have been a transferred use of the surname derived from the medieval given name, and later to have been taken as a pet form of Terence.
English and Scottish: occupational name for a tailor, from Old French tailleur (Late Latin taliator, from taliare ‘to cut’). The surname is extremely common in Britain and Ireland, and its numbers have been swelled by its adoption as an Americanized form of the numerous equivalent European names, most of which are also very common among Ashkenazic Jews, for example Schneider, Szabó, and Portnov.