The meaning is unknown. A literary invention, first appeared in the Swedish novel Kyrkoinvigningen i Hammarby (1840-1841) by Emilie Flygare-Carlén. Author Marie Corelli used it for her Norwegian heroine in the 1887 novel Thelma. The name became quite popular at end of the 19th century. Some sources claim Thelma is derived from Greek θελημα (thelema) meaning "will", but it's not likely. Mostly the name was part of a trend for similar-sounding names of ambiguous origin, (Elma, Selma, Velma, Wilma) which also appeared in the 19th century.
There is no Hebrew name for Thelma. In fact, no one knows where the name came from or what it means. When it was first used in print in 1887, it was considered a rare name.
Thelma Ruby's birth name is Thelma Wigoder.
Thelma McGough's birth name is Thelma Pickles.
Thelma Hill's birth name is Hillerman, Thelma.
Thelma Hardwick's birth name is Thelma Daniels.
Thelma White's birth name is Thelma Wolpa.
Thelma Barlow's birth name is Thelma Pigott.
Thelma Leeds's birth name is Thelma Goodman.
Thelma Tixou's birth name is Thelma Delia Suklenik.
Thelma Stefani's birth name is Thelma Nlida Stefani.
Thelma Brown's birth name is Thelma D. Brown.
Thelma Raye's birth name is Thelma Victoria Maud Raye.