thud in WordNet English dictionary

1. a heavy dull sound (as made by impact of heavy objects)
   thump  thumping  clump  clunk  thud 
   

1. make a noise typical of an engine lacking lubricants
   crump  thud  scrunch 
   
2. strike with a dull sound
   "Bullets were thudding against the wall"
   thud 
   
3. make a dull sound
   "the knocker thudded against the front door"
   thud  thump