Teresa - Theresa

The two spellings Teresa and Theresa are variants of the same female forename. The preferred RP pronunciation has the stress on the middle vowel, a long '-e-' as in 'sea' or 'be': 'ter-EASE-ah', IPA: /tər ˈiːz ə (or a)/. Sometimes this is realized as 'raise', /tər ˈeɪz ə (or a)/.

Be careful to spell the name of people you are studying or quoting in the way they prefer. 

Of the two spellings, Teresa, the Spanish and Italian form, may be more popular among Roman Catholics because of that church's veneration of Saint Teresa of Ávila (1515-82), but another popular saint used the French form, Thérèse - St. Therese of Lisieux, (1873-1897). The traditional spelling in English was Theresa, probably influenced by the Austrian spelling of the name of the Austro-Hungarian Empress Maria Theresa (1717–1780), the only female ruler of the Habsburg dominions and the last of the House of Habsburg (although the usual form in German is Maria Theresia). She was a formidable figure in European politics throughout her forty year reign, She was the mother of Marie Antoinette. The name Maria Theresa has been given to many members of the Habsburg royal house, and to their multitudinous connections.

• The second female Prime Minister of the UK was Mrs Theresa May (1956 - present; PM 2016-2019).

Etymological note: the origin of T[h]eresa is obscure. Wikipedia says "The name may be derived from the Greek verb θερίζω (therízō), meaning to harvest", while Hanks, Hardcastle and Hodges (2006) say "The name seems to have been first used in Spain and Portugal, and, according to tradition, was the name of the wife of St Paulinus of Nola, who spent most of his life in Spain; she was said to have originated (and to have derived her name) from the Greek island of Thēra. However, this story is neither factually nor etymologically confirmed."

See also Saint Theresa.