1. sits or falls down heavily and suddenly
2. places something down heavily or carelessly
3. makes something fuller or rounder by shaking or adjusting

Examples

• She plumps down in the chair after a long day.
• He plumps the heavy bag on the table.
• The cat plumps onto the sofa and starts purring.
• She plumps the pillows before the guests arrive.
• The tired hiker plumps down beside the trail.
• He plumps his backpack in the corner of the room.