Green’s Dictionary of Slang

1. (US und.) a prostitute operating without a pimp.

1938

J. O’Hara Hope of Heaven 98: I immediately recognized the girl with him, and so would have at least half the men in the room. She was one of the girls; a free-lance.

2. a habitual adulteress, although not a professional prostitute.

1949

Monteleone Criminal Sl. (rev. edn).