If you plump a pillow or cushion, you shake it and hit it gently so that it goes back into a rounded shape. She panics when people pop in unexpectedly, rushing round plumping cushions. Plump up means the same as plump. `You need to rest,' she told her reassuringly as she moved to plump up her pillows
the sound of a sudden heavy fall give support (to) or make a choice (of) one out of a group or number; "I plumped for the losing candidates"
You can describe someone or something as plump to indicate that they are rather fat or rounded. Maria was small and plump with a mass of curly hair red pears, ripe peaches and plump nectarines. + plumpness plump·ness There was a sturdy plumpness about her hips