(derogatory) To live together, especially of an unmarried couple.

simple past tense and past participle of shack up

Sharing a small room or accommodation between many (often too many) people / (idiomatic) (of a couple) Sharing a house, but not married.

present participle of shack up

A roadside restaurant that sells cooked clams as a snack.

(slang, nautical) A room for hosting radio equipment.

(UK, law) The right of persons occupying lands lying together in the same common field to turn out their cattle to range in it after harvest.

plural of shack rat

(slang, military) A female civilian visiting military barracks in order to have sex with soldiers. / (slang, military) A female civilian cohabitating with a male soldier.

(slang) Mental hospital.