Possibly from Greek 'therizein' meaning 'to harvest', or from the Greek island Thera.
Theresa is a classic European form of Teresa, a name whose exact origin remains one of the more tantalizing mysteries in onomastics. It appears in late antique Christian records as Therasia, and scholars have connected it variously with Greek theros, meaning "summer," with a verb meaning "to harvest," or with the Aegean place-name Therasia near Santorini. That uncertainty has not weakened the name; if anything, it has given Theresa an aura of age and depth, as though it stands at the meeting point of language, geography, and devotion.
Its fame spread decisively through religion. Saint Teresa of Ávila, the 16th-century Spanish mystic, reformer, and author, transformed the name into one of Catholic Europe’s great spiritual names. In the German-speaking and English-speaking worlds, Theresa became a common spelling, and it was further dignified by figures such as Empress Maria Theresa of Austria.
In more recent public life, Theresa May gave the name a modern political face. Through all of these bearers, Theresa has carried connotations of seriousness, discipline, intellect, and moral force. Usage has shifted over time.
Once a staple across Christian Europe and America, Theresa peaked in an era when saintly and dynastic names held strong prestige, then gradually receded as shorter and less formal names took over. Yet it has never vanished. It remains richly furnished with literary and devotional echoes, from convent chronicles to imperial history. Theresa feels traditional, but not fragile: its sound is gentle, while its historical record is unexpectedly formidable.