Green’s Dictionary of Slang

shack-up n.

[shack up (with) v.]

1. (US, also shack) a person with whom one has a sexual relationship; also attrib.

[US]L. Uris Battle Cry (1964) 192: The men drank and slept with their shackups.
[US]J. Crumley One to Count Cadence (1987) 62: His steady shack, Dottie the bow-legged whore.
[Can](con. 1920s) O.D. Brooks Legs 225: You’ll get pieced off like a shack-up broad.

2. an act of sexual intercourse; also attrib.

[UK]W. Eyster Far from the Customary Skies 58: I’d sure like one shack-up job before we go across.
[US]E. Shepard Doom Pussy 168: He’s just come back from a shack-up with her somewhere.
[US]B. Davidson Collura (1978) 100: A one-night shack-up at the Beverley Hills Hotel during a vacation.

3. a sexual relationship.

[US] in T.I. Rubin Sweet Daddy 96: They want it all [...] shack ups, gang bangs, sandwiches, the works.
[US]A. Maupin Tales of the City (1984) 59: For God’s sake! This isn’t a shack-up!
[US]A. Maupin Further Tales of the City (1984) 28: I paid for a weekend shack-up in Sierra City.