late 14c., "formal authorization, official permission, permit, privilege," from Old French licence "freedom, liberty, power, possibility; permission," (12c.), from Latin licentia "freedom, liberty; unrestrained liberty, wantonness, presumption," from licentem (nominative licens), present participle of licere "to be allowed, be lawful," from PIE root *leik- "to offer, bargain, make a bid" (possibly source also of Lettish likstu "I come to terms").
Meaning "formal (usually written) permission from authority to do something" (marry, hunt, drive, etc.) is first attested early 15c. Meaning "excessive liberty, disregard of propriety" in English is from mid-15c. In Middle English spelled licence, licens, lisence, lissens, licance. There have been attempts to confine license to verbal use and licence to noun use (compare advise/advice, devise/device, and see note in OED); in the U.S., license tends to serve as both verb and noun.
Poetic licence "intentional deviation from recognized form or rule" is from 1733, earlier as lycence poetycall (1530). The licence-plate is from 1870 (of dogs and wagons before automobiles); licence-number is by 1903.
"morally unrestrained," 1530s, from Medieval Latin licentiosus "full of licence, unrestrained," from Latin licentia "freedom, liberty," in both a good and bad sense (see licence (n.)). Related: Licentiously; licentiousness.
Especially "opportunity afforded by freedom from necessary occupations" (late 14c.). "In Fr. the word has undergone much the same development of sense as in Eng." [OED]. The -u- appeared 16c., probably on analogy of pleasure (n.), etc. To do something at leisure "without haste, with deliberation" (late 14c.) preserves the older sense. To do something at (one's) leisure "when one has time" is from mid-15c.
"written statement of permission or licence, written authority to do something," 1714, from permit (v.).