Sense evolved in English and French to "having the character or manners of one of noble rank or birth," varying according to how those were defined. From mid-13c. in English as "gracious, kind" (now obsolete), manners prescribed for Christian or chivalrous nobility. From late 13c. as "courteous, polite, well-bred, charming;" c. 1300 as "graceful, beautiful." Meaning "mild, tender; easy; not harsh" (of animals, things, persons) is from 1550s. Older sense remains in gentleman, and compare gentile (adj.), an alternative form which tends to keep the Biblical senses of the Latin word (though gentle in Middle English sometimes meant "pagan, heathen"), and genteel, which is the same word borrowed again from French. From 1823 as "pertaining to the fairies."
"extremely cautiously" (of movements, etc.), c. 1600; earlier "elegantly, daintily" (1510s), of unknown origin. Perhaps [OED] from Old French gensor, comparative of gent "dainty, delicate," from Latin gentius "(well)-born" (see gentle).
1590s, "fashionably elegant; suitable to polite society, characteristic of a lady or gentleman; decorous in manners or behavior," from French gentil "stylish, fashionable, elegant; nice, graceful, pleasing," from Old French gentil "high-born, noble" (11c.); a reborrowing (with evolved senses) of the French word that had early come into English as gentle (q.v.), with French pronunciation and stress preserved to emphasize the distinction. The Latin source of the French word is the ancestor of English gentile, but the main modern meaning of that word is from a later Scriptural sense in Latin. See also jaunty. OED 2nd ed. reports genteel "is now used, except by the ignorant, only in mockery" (a development it dates from the 1840s).