blunder
n. countablen. a big or careless mistake. You use this when someone does something wrong because they were not thinking or were not careful.
n. a gross, stupid, or careless mistake resulting from ignorance or lack of deliberation.
The goalkeeper made a terrible blunder in the final minute.
The company's decision to ignore the new market trends proved to be a costly blunder that led to bankruptcy.
Historians often debate whether the general's choice to divide his forces was a calculated risk or a strategic blunder that doomed the entire campaign.
Inherited from Middle English blundren, blondren (verb) and blunder, blonder (“disturbance, strife”), from the verb; partly from Middle English blondren, a frequentative form of Middle English blonden, blanden ("to mix; mix up"; corresponding to blend + -er); and partly from Middle English blundren, a frequentative form of Middle English blunden (“to stagger; stumble”), from Old Norse blunda (“to shut the eyes; doze”). Cognates include Norwegian blunda (“to shut the eyes; doze”), dialectal Swedish blundra (“to act blindly or rashly”), Danish blunde (“to blink”) or blunde (“to take a nap”), Icelandic blunda (“to nap; doze”). Related to English blind.
Often modified by adjectives like 'costly', 'tactical', or 'fatal'.