Entries linking to gently
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."
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.