As a Noun: 1. A relationship in which two people live together in a sexual and domestic relationship without there being any act of marriage (legal, civil, or religious) between them. English = de facto relationship. 2. A person who lives with another person in a sexual and domestic relationship (as husband or wife) without there being any act of marriage (legal, civil, or religious) between them. English = de facto. As a Verb or Adjective: 1. To live with someone in a sexual and domestic relationship without there being any act of marriage (legal, civil, or religious) between you. English = (be) de facto. Idiomatic English = shack up with/together, live together. 2. To have a casual sexual relationship with someone. Idiomatic English = go to bed with someone.