Origin and history of implicitly

1590s, "implied, resting on inference," from French implicite and directly from Latin implicitus, later variant of implicatus "entangled, confused, involved," past participle of implicare "entangle, involve," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + plicare "to fold" (from PIE root *plek- "to plait"). From c. 1600 as "resulting from perfect confidence (in authority), unquestioning" (especially of faith).

"plainly, without disguise or reservation of meaning, not by inference; clearly, unmistakably," 1630s, from explicit + -ly (2). Opposed to implicitly.

common adverbial suffix, forming, from adjectives, adverbs signifying "in a manner denoted by" the adjective; Middle English -li, from Old English -lice, from Proto-Germanic *-liko- (source also of Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko). See -ly (1). It is 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.