hastily (adv.)

mid-14c., "early; demanding haste, urgent; quick-tempered, angry;" late 14c. "speedy, swift, quick," by 1500s, from haste (n.) + -y (2); replacing or nativizing earlier hastif (c. 1300) "eager, impetuous," from Old French hastif "speedy, rapid; forward, advanced; rash, impetuous" (12c., Modern French hâtif), from haste (see haste (n.)). Meaning "requiring haste" is late 14c. (this is the sense in hasty-pudding, 1590s, so called because it was made quickly); that of "eager, rash" is from early 15c. Related: Hastiness. Old French also had a form hasti (for loss of terminal -f, compare joli/jolif, etc.), which may have influenced the form of the English word.

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.