D defs.my
Entry 2 senses Webster, 1913

Shack up

· Shack· up · IPA
01 v. i. to live together in a sexual relationship, without being legally married.
  1. 1.
    to live together in a sexual relationship, without being legally married.[Slang, U. S.]
  2. 2.
    to live in a cabin, shack, or other crude dwelling.[Slang, U. S.]