late 14c., of persons, "self-indulgent, loving ease;" also "sensitive, easily hurt, feeble;" of things, "delightful," from Latin delicatus "alluring, delightful, dainty," also "addicted to pleasure, luxurious, effeminate," in Medieval Latin "fine, slender;" related to deliciae "pleasure, delight, luxury," and delicere "to allure, entice," from de "away" (see de-) + lacere "to lure, entice," which is of uncertain origin. Compare delicious, delectable, delight.
Meaning "so fine or tender as to be easily broken" is recorded from 1560s. Meaning "requiring nice and skillful handling" is by 1742. Sense of "exquisitely adjusted in construction" is from 1756. Related: Delicateness.
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.