Merriam-Webster's Collegiate® Dictionary, 11th Edition
QUIT
I. adjective
Etymology: Middle English quite, quit, from Anglo-French
Date: 13th century
released from obligation, charge, or penalty,
II. verb (quit; also quitted; quitting)
Etymology: Middle English quiten, quitten, from Anglo-French quiter, from quite free of, released, from Latin quietus quiet, at rest
Date: 13th century
transitive verb to make full payment of ; pay up , to set free ; relieve , release , conduct , acquit ,
4. to depart from or out of, to leave the company of, give up 1 , give up 2 , intransitive verb to cease normal, expected, or necessary action , to give up employment, to admit defeat ; give up , see: stop
III. noun
Date: circa 1923
the act or an instance of quitting a job