well rounded or filled out; full; fleshy; fat; as, a plump baby; plump cheeks.-a knot; a cluster; a group; a crowd; a flock; as, a plump of trees, fowls, or spears.-to grow plump; to swell out; as, her cheeks have plumped.-to drop or fall suddenly or heavily, all at once.-to give a plumper. see plumper, 2.-to make plump; to fill (out) or support; -- often with up.-to cast or let drop all at once, suddenly and heavily; as, to plump a stone into water.-to give (a vote), as a plumper. see plumper, 2.-directly; suddenly; perpendicularly.