word meaning "friend, brother, and/or lover". First used in the novelisation of Star Trek: The Motion Picture, the word was created by Gene Roddenberry to describe the relationship between Captain Kirk and Spock.
An excerpt from the novel says "Editor’s note: The human concept of friend is most nearly duplicated in Vulcan thought by the term t’hy’la, which can also mean brother and lover."
T'hy'la is popularly used in Kirk/Spock slash
stories, where "soul-mate" and "life-long companion" are often accepted within fanon
as additional definitions of T'hy'la.
Jim! Good-bye my . . . my t'hy'la. This is the last time I will permit myself to think of you or even your name again.
-- Spock's thoughts before almost undergoing Kolinahr, a Vulcan ritual to purge all emotion. (Star Trek: The Motion Picture novel, page 14-15.)
There was much to be put out of his mind. Why was it difficult to forget Chekov’s astonished delight which greeted him at the command airlock when he boarded? And on the bridge—Kirk! The mere name made Spock groan inwardly as he remembered what it had cost him to turn away from that welcome. T'hy'la!
-- (Star Trek: The Motion Picture novel, page 109.)