Green’s Dictionary of Slang

thesp n.

an actor.

[1915		O.O. McIntyre New York Day by Day 24 July [synd. col.] Harry Langdon, a vaudeville thespian, who thesps on the Big Time].
1962		New Statesman 23 Feb. 274/3: Like all tales about thesps, [it] seems to involve us just that much less in their fate .
1970		T. Southern Blue Movie (1974) 29: It was a grand job of weeping, thesp-wise.
1999		Indep. Rev. 2 July 4: A 54-year-old Californian thesp.
2000		Indep. on Sun. Real Life 23 Jan. 3: Tormented footballer turned thesp.
2023		R. Milward Man-Eating Typewriter 381: [T]he bourgeois thesps and fox-furred binocular toffs.

In derivatives

thespy (adj.)

affected (as a neg. stereotype).

1999

Indep. on Sun. Real Life 15 Aug. 3: Dobson is your genuine thespy sort [...] She’s trodden the boards in proper theatre.