mid-14c., "to stumble about blindly," from a Scandinavian source akin to Old Norse blundra "shut one's eyes," perhaps from Proto-Germanic *blinda- "blind" (see blind (adj.)). The meaning "make a stupid mistake" is recorded by 1711. Related: Blundered; blundering.
late 14c., blonder, blunder, "disturbance, strife; trouble, distress;" apparently from blunder (v.). The original sense is obsolete. The meaning "a mistake made through hurry or confusion" is from 1706.
mid-14c., present-participle adjective from blunder (v.). Related: Blunderingly. As a verbal noun, mid-15c.
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."
"short, large-bore gun or firearm with a funnel-shaped muzzle," 1650s, from Dutch donderbus, from donder "thunder" (Middle Dutch doner, donder, from Proto-Germanic *thunaraz; see thunder (n.)) + bus "gun" (originally "box, tube"); altered by resemblance to blunder. Related: Blunderbussier.
"to flounder, blunder," 1530s, probably of imitative origin. Related: Bumbled; bumbler; bumbling. Bumble-puppy (1801) was a name for various outdoor sports and games.
"blunder," 1909, perhaps from French gaffe "clumsy remark," originally "boat hook" (15c.), from Old Provençal gafar "to seize," probably from a Germanic source, from Proto-Germanic *gaf-, which is perhaps from PIE root *kap- "to grasp." Sense connection between the hook and the blunder is obscure; the gaff was used to land big fish. Or the Modern English word might derive from British slang verb gaff "to cheat, trick" (1893); or gaff "criticism" (1896), from Scottish dialect sense of "loud, rude talk" (see gaff (n.2)).