1610s, verb and noun, perhaps from Scandinavian, probably echoic, original sense was "hitting" then of "swelling from being hit." Also has a long association with obsolete bum "to make a booming noise," which perhaps influenced surviving senses like bumper crop, for something full to the brim. To bump into "meet" is from 1880s; to bump off "kill" is 1908 in underworld slang.
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with bump off
Kill, murder, as in The convict bragged about bumping off his partner, or The first fighter plane bumped off three enemy aircraft. This term was at first principally criminal slang and somewhat later military jargon.
[ ; c. 1900