shack up

verb

1. slang,  to live or take up residence, esp with a mistress or lover

Idioms and Phrases

Sleep together or live in sexual intimacy without being married. For example, They had been dating for two months and then decided to shack up . [ Slang ; first half of 1900s]

Stay or reside with, as in I'm shacking up with my cousin till I find a place of my own . [ Slang ; first half of 1900s]