To set, throw, drop, or place someone, something, or oneself heavily down to a lower level. A variant of the more common "plunk (someone, something, or oneself) down." He plonked the bag on the table and went into his room without a word. Please don't just plonk yourself down in front of the television all afternoon—I want you to play outside for at least two hours today! He threw his toy across the room, so I carried him upstairs kicking and screaming and plonked him down in bed for the night.

To fall or set down heavily down to a lower level. A variant of the more common "plunk (someone, something, or oneself) down." He came into the room and plonked down onto the sofa, too tired to speak. Please don't just plonk down in front of the television all afternoon—I want you to play outside for at least two hours today!