Green’s Dictionary of Slang

a temporary worker, usu. a secretary; also attrib.

1932		‘Speech in the Post Office’ AS VII:4 278: A temp, a part-timer.
1975		L. Rosten Dear ‘Herm’ 101: So I have a new ‘Tempo’ who looks O.K. as a girl Friday.
1979		F. Norman Too Many Crooks Spoil the Caper 194: I’m a temp from the Bizzy Bee secretarial agency.
1986		B. Geldof Is That It? 67: Daphne earned a fair wage typing as a temp.
1997		Simon & Burns Corner (1998) 405: He’d filled out a few applications at some of the temp places too.