A colloquial term for early diesel-electric multiple unit passenger trains, named for the distinct, low-frequency rhythmic thumping sound produced by their four-cylinder diesel engines. These units were heavily used on non-electrified branch lines in the UK, but the term is occasionally applied by North American mechanics to any older, rough-idling diesel engine that shakes the carbody.
Heard on the job
They assigned us that old thumper for the branch line run, so bring your earplugs.