Concubinage

/ˈkɒn.kjʊ.bɪ.nɪdʒ/

Synonyms

  • cohabitation
  • extramarital relationship
  • mistressship
  • paramourship

Slang Meanings

Shacking up
They've been shacking up for years without tying the knot.
Live-in partner
He considers her his live-in partner, but they aren't officially married.