Thomasina or Thomasine is the feminine form of the given nameThomas, which means "twin".
Thomasina is often shortened to Tamsin. Tamsin can be used as a name in itself; variants of Tamsin include Tamsyn, Tamzin, Tamsen, Tammi and Tamasin. Although Aramaic in origin, the version "Tamsin" is especially popular in Cornwall and Wales. Along with Tamara it is the ancestor of "Tammy".