bluntly (adv.)

c. 1200, blunt, blont, "dull, obtuse" (of persons), of uncertain origin. Perhaps from or related to Old Norse blundra "to shut one's eyes" (see blunder (v.)). Or from Old English blinnan (past participle blon) "to stop, cease, come to an end." Of tools or weapons, "not sharp, without edge or point," late 14c. The meaning "abrupt of speech or manner" is from 1580s. Late 18c. Scottish writers used blunty (n.) for "stupid fellow."

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.