COHABIT
coexist, cohabit
(verb) exist together
cohabit, live together, shack up
(verb) share living quarters; usually said of people who are not married and live together as a couple
Source: WordNet® 3.1
Etymology
Verb
cohabit (third-person singular simple present cohabits, present participle cohabiting, simple past and past participle cohabited)
(intransitive) To live together with someone else, especially in a romantic and sexual relationship but without being married.
(intransitive) To coexist in common environs with.
(intransitive, archaic) To engage in sexual intercourse; see coition.
Synonyms
• (to live together with someone else): cohabitate
• (to engage in sexual intercourse): fornicate, have sex, make love; see also copulate
Source: Wiktionary
Co*hab"it, v. i. [imp. & p. p. Cohabited; p. pr. & vb. n.
Cohabiting.] Etym: [L. cohabitare; co- + habitare to dwell, to have
possession of (a place), freg. of habere to have. See Habit, n. & v.]
1. To inhabit or reside in company, or in the same place or country.
The Philistines were worsted by the captived ark . . . : they were
not able to cohabit with that holy thing. South.
2. To dwell or live together as husband and wife.
The law presumes that husband and wife cohabit together, even after a
voluntary separation has taken place between them. Bouvier.
Note: By the common law as existing in the United States, marriage is
presumed when a man and woman cohabit permanently together, being
reputed by those who know them to be husband and wife, and admitting
the relationship. Wharton.
Source: Webster’s Unabridged Dictionary 1913 Edition