THERESA.  Antonio says it is found written Tarasia, and that there is a masculine Tarasius.  Stephanus gives a Ταράσιος (Tarasios); and also a Ταρασἰα, which he refers to the name of a vates, perhaps from τειρεσια, divinatio.  Others derive the name Theresa from θηραω, to hunt; and it might even be the same as Threissa mentioned by Virgil, and Thressa referred to by Horace, the same as Θρήσσα, feminine of Θρήξ, Ionic for Θράξ, a Thracian.  It might also be derived from Therasia, an island near Crete, mentioned by Strabo and Pliny; or from Therasia, another island spoken of by the latter, first called Lipara and finally Hiera.  But see also Antonio, Bibliotheca Hispana Vetus, ed. 1788, tom. 1, p. 160, No. 80.  The nickname is Tracy. (Praenomina, Charnock, 1882).

... From θέρω (to heat) was derived θέρος (summer), which, in sunny Greece, came likewise to mean the summer crop, just as in Germany Herbst serves for both autumn and harvest.  θερίζω (to reap or gather in the crop), and from this verb comes the pretty feminine Theresa, the reaper.  "The first to bear the predestined name of Theresa," as Montalembert says, was a Spanish lady, the wife of a Roman noble called Paulinus, both devotees under the guidance of St. Jerome, whose writings most remarkably stamped the memory of his friends upon posterity; and this original Theresa was copied again and again by her own countrywomen,...
    The real popularity of the word, witnessed by its many changes of sound, is, be it observed, in those Eastern domains of the empress where her noble spirit won all hearts to the well-remembered cry "Moriamur pro Rege nostrâ Maria Theresa." (History of Christian Names, Yonge, 1884)