Old English bær "naked, uncovered, unclothed," from Proto-Germanic *bazaz (source also of German bar, Old Norse berr, Dutch baar), from PIE *bhoso- "naked" (source also of Armenian bok "naked;" Old Church Slavonic bosu, Lithuanian basas "barefoot"). Meaning "sheer, absolute" (c. 1200) is from the notion of "complete in itself."
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.
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Harper, D. (n.d.). Etymology of barely. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/barely