As soon as a car was dumped, the dumper would call out "clear," whereupon the motor-man would shove his train forward.
early 14c., "throw down or fall with force," perhaps from a Scandinavian source (cf. Danish dumpe, Norwegian dumpa "to fall suddenly"). The sense of "unload en masse" is first recorded in American English 1784. That of "discard, abandon" is from 1919. Related: Dumped; dumping. Dump truck is from 1930.
"place where refuse is dumped," 1865, originally of mining operations, from dump (v.). Meaning "any shabby place" is from 1899. Meaning "act of defecating" is from 1942.
[origin uncertain; perhaps related to a Scandinavian term meaning ''to fall suddenly,'' the connection being the tipping out of a load from a cart]