What is the meaning of thud?

noun

• A heavy dull sound (as made by impact of heavy objects.
  • synonyms: thump, thumping, clump, clunk

verb

• Make a dull sound.
  • usage: "the knocker thudded against the front door"
  • synonyms: thump
• Strike with a dull sound.
  • usage: "Bullets were thudding against the wall"
• Make a noise typical of an engine lacking lubricants.
  • synonyms: crump, scrunch