|Origin:||Copying the action|
1 also plump up [transitive]
to make cushions, pillows etc rounder and softer by shaking or hitting them
to sit down suddenly and heavily [= plonk]
3 [transitive always + adverb/preposition]
to put something down suddenly and carelessly [= plonk]:
Plump the bags down anywhere you like.
4 also plump up [intransitive and transitive]
if dried fruit plumps up, or if you plump it up, it becomes fatter and softer when in liquid:
Soak the apricots and raisins until the fruit plumps up.
plump for something/somebodyphrasal verb
Finally we plumped for a bottle of champagne.