"even" (with another), 1660s; earlier "discharged of a liability" (c.1200), perhaps from Medieval Latin quittus (see quit (adj.)).
To stop or terminate something; declare one has had enough: The Iraqi leadership has hunkered down; time to call it a day/ Any sensible assassin would have called it quits
[first form 1840s+, second 1940s+; Call quits is attested from the 1890s]