early (adv.)

c. 1200, from Old English ær (adv., conj., & prep.) "soon, before (in time)," from Proto-Germanic *airiz, comparative of *air "early" (source also of Old Saxon, Old Frisian, Old High German er, Dutch eer; German eher "earlier;" Old Norse ar "early;" Gothic air "early," airis "earlier"), from PIE *ayer- "day, morning" (source also of Avestan ayar "day;" Greek eerios "at daybreak," ariston "breakfast"). The adverb erstwhile retains the Old English superlative ærest "earliest."

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.