A blunder is an embarrassing mistake. Accidentally called your new boyfriend by your old boyfriend's name? Ouch. That's a blunder you don't want to repeat.
Has an embarrassing mistake ever made you feel like you’re stumbling around with your eyes closed? If so, it won’t surprise you to learn that blunder comes from the Old Norse word blundra, meaning to “shut one's eyes.” It wasn’t until the eighteenth century that blunder came to refer to a stupid or embarrassing mistake, or as a verb, to describe making such a mistake, as in “I tend to blunder when I'm nervous.”