boo-boo \ˈbüˌbü\noun (-s) Etymology: probably baby-talk alteration of boohoo 1.dialect: a usually minor physical injury (as a bruise or scratch) especially on a child < he fell down and he's got a boo-boo on his forehead > 2.slang: a foolish or embarrassing error : a stupid or careless mistake : blunder, boner < committed a boo-boo at his press conference >