blunder

Concise Oxford English Dictionary © 2008 Oxford University Press:
blunder/ˈblʌndə(r)/

▶noun a stupid or careless mistake. ▶verb

• 1 make a blunder.

• 2 move clumsily or as if unable to see.

– derivatives
blunderer noun,
blundering adjective,
blunderingly adverb.

– origin ME: prob. of Scand. origin and rel. to blind.