Merriam-Webster's Collegiate® Dictionary, 11th Edition
BUMP
I. noun
Etymology: probably imitative of the sound of a blow
Date: 1581
a relatively abrupt convexity or protuberance on a surface: as, a swelling of tissue, a cranial protuberance,
2. a sudden forceful blow, impact, or jolt, demotion, an act of thrusting the hips forward in an erotic manner,
II. verb
Date: 1581
transitive verb to strike or knock with force or violence, to collide with,
3. a. to dislodge with a jolt, to subject to a scalar change , to oust usually by virtue of seniority or priority , intransitive verb to knock against something with a forceful jolt, to proceed in or as if in a series of bumps, to encounter something that is an obstacle or hindrance