To make a loud, heavy, or hollow noise, as the bittern; boom.n. A booming, hollow noise.To cause to come in violent contact; bring into concussion; knock; strike; thump: as, to bump one's head against a wall.In English boat-racing, to touch (the stern of a boat ahead) with the bow of the following boat. See extract.To come forcibly in contact with something; strike heavily: as, the vessel bumped against the wharf.To ride without rising in the stirrups on a rough-trotting horse.In chem., to give off vapor intermittently and with almost explosive violence, as some heated solutions.To form bumps or protuberances.n. A shock from a collision, such as from the jolting of a vehicle.n. In English boat-racing, the striking of one boat by the prow of another following her. See bump, transitive verb, 2.n. A swelling or protuberance, especially one caused by a blow.n. Specifically The popular designation of the natural protuberances on the surface of the skull or cranium, which phrenologists associate with distinct qualities, affections, propensities, etc., of the mind: used ironically for the word organ employed by phrenologists: as, the bump of veneration, acquisitiveness, etc.n. The corner of the stock of a gun at the top of the heel-plate.n. A material used for coarse sheets.n. In London, a sort of matting used for covering floors.n. In cricket, the act of rising higher than usual from the pitch after being bowled: said of the ball.