lustily adv.

early 13c., "joyful, merry;" late 14c., "full of healthy vigor," from lust (n.) + -y (2). Used of handsome dress, fine weather, good food, pleasing language, it largely escaped the Christianization and denigration of the noun in English. The sense of "full of desire" is attested from c. 1400 but seems to have remained secondary. Related: Lustily; lustiness.

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.