Definitions:

1. set something down with or as if with a noise verb
   • I plopped it down with such force that it startled my dog.
2. with a short hollow thud adverb
   • plop came the ball down to the corner of the green

Synonyms:

• flump
• plank
• plonk
• plump
• plump down
• plunk
• plunk down