overtly (adv.)

early 14c., "open; unfastened" (originally literal, of clothing, a book, etc.; this sense is now obsolete), from Old French overt (Modern French ouvert), past participle of ovrir "to open," from Latin aperire "to open, uncover," from PIE compound *ap-wer-yo- from *ap- "off, away" (see apo-) + root *wer- (4) "to cover." Compare Latin operire "to cover," from the same root with PIE prefix *op- "over;" and Lithuanian atverti "open," užverti "shut." The meaning "clear, open or plain to view, manifest, revealed" is from late 14c.

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.