late 15c., "stupidity," also "dullness of an edge, state or quality of being blunt," from blunt (adj.) + -ness. The meaning "rudeness" is from c. 1600.
Entries linking to bluntness
blunt adj.
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."
-ness
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).