Definition of "thumper"

One who thumps.  examples

(slang) A single-cylinder engine, especially four-stroke engines or those with large engine displacements.

(uncountable) A drinking game wherein players must remember personal hand signs while being distracted by others banging on a table.  examples

(slang) Something big, such as a lie; a whopper.

(UK, rail transport, slang) A kind of slam-door train introduced in the late 1950s.

(US, military, slang) The Vietnam-era M79 grenade launcher (due to its distinctive report).