n.
   - a light blow or a jolting collision. ▸Rowing  (in races where boats make a spaced start one behind another) the point at which a boat begins to overtake or touch the boat ahead, thereby defeating it. 
- a protuberance on a level surface. ▸dated a lump on a person's skull, formerly thought to indicate a particular mental faculty. 
- Aeronautics  a rising air current causing an irregularity in an aircraft's motion.
v.
     - knock or run into with a jolt. ▸
(bump into)
 meet by chance. ▸Rowing  gain a bump against. 
- move or travel with much jolting.
- 
(bump someone off)
 informal murder someone.
- 
(bump something up)
 informal make something larger or appear to be larger.
- refuse (a passenger) a reserved place on a flight because of deliberate overbooking by the airline. ▸N. Amer. displace from a job or position. 
Etymology
  C16 (as v.): imitative, perh. of Scand. origin.