intransitive verb
slang : to become established in a dwelling or shelter especially when involving cohabitation : spend the night : cohabit — often used with with
he shacked up with another girl he knew — Wenzell Brown
transitive verb
slang : to establish in a dwelling or shelter especially when involving cohabitation
were shacked up comfortably inside bamboo huts — Infantry Journal
the girls get boyfriends who shack them up for a time — Marya Mannes