fluff up verb 2fluff-up noun 1forms 4 verb2 •To plump up.Fluff up the pillows to get the bed ready for guests. •(slang) To make a gaffe or blunder; to fuck up.I fluffed up on that tricky ski jump. fluff-up noun1 •A blunder.On top of that he upset the frying-pan with an almighty fluff-up of blazing fat, and exploded into curses. — 1938 formsfluffed up · fluffing up · fluffs up · fluff-ups