goof up verb 2goof-up noun 1forms 4 verb2 •(slang) To make a mistake.If I go near a skateboard, I'm sure I'm just going to goof up and fall off. •(slang) To introduce problems to or damage through incompetence.I tried to fix it, but I think I just goofed it up some more. goof-up noun1 •(slang) A mistake or problem.The letter they sent was a goof-up; it was intended for someone else. formsgoofed up · goofing up · goofs up · goof-ups