Blunder

v. make a stupid mistake; move back and forth in a clumsy manner, move blindly, grope

n. gross error, stupid mistake

A blunder is a spectacularly bad decision or action, a mistake or error with detrimental consequences to the party that makes it. It is typically attributable to faulty perception: the result of not reading signs, or misinterpreting available information. Naturally many sensible decisions, which even in retrospect were carefully taken, may also prove disastrous mistakes.
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Noun
1. an embarrassing mistake
(synonym) blooper, bloomer, bungle, foul-up, fuckup, flub, botch, boner, boo-boo
(hypernym) mistake, error, fault
(hyponym) snafu
(derivation) sin, boob, goof
Verb
1. commit a faux pas or a fault or make a serious mistake; "I blundered during the job interview"
(synonym) sin, boob, goof
(hypernym) transgress, offend, infract, violate, go against, breach, break
(derivation) bungler, blunderer, fumbler, bumbler, stumbler, sad sack, botcher, butcher, fuckup
2. make one's way clumsily or blindly; "He fumbled towards the door"
(synonym) fumble
(hypernym) pass, go through, go across
3. utter impulsively; "He blurted out the secret"; "He blundered his stupid ideas"
(synonym) blurt out, blurt, blunder out, ejaculate
(hypernym) talk, speak, utter, mouth, verbalize, verbalise

n. blunder, gaffe, stupid mistake

v. blunder, make a stupid mistake

(v. t.)
To do or treat in a blundering manner; to confuse.
  

(v. t.)
To cause to blunder.
  

(v. i.)
To move in an awkward, clumsy manner; to flounder and stumble.
  

(v. i.)
To make a gross error or mistake; as, to blunder in writing or preparing a medical prescription.
  

(n.)
Confusion; disturbance.
  

(n.)
A gross error or mistake, resulting from carelessness, stupidity, or culpable ignorance.