Source : Webster's Revised Unabridged Dictionary (1913)

Rump \Rump\, n. [OE. rumpe; akin to D. romp trunk, body, LG.
   rump, G. rumpf, Dan. rumpe rump, Icel. rumpr, Sw. rumpa rump,
   tail.]
   1. The end of the backbone of an animal, with the parts
      adjacent; the buttock or buttocks.

   2. Among butchers, the piece of beef between the sirloin and
      the aitchbone piece. See Illust. of {Beef}.

   3. Fig.: The hind or tail end; a fag-end; a remnant.

   {Rump Parliament}, or {The Rump} (Eng. Hist.), the remnant of
      the Long Parliament after the expulsion by Cromwell in
      1648 of those who opposed his purposes. It was dissolved
      by Cromwell in 1653, but twice revived for brief sessions,
      ending finally in 1659.

            The Rump abolished the House of Lords, the army
            abolished the Rump, and by this army of saints
            Cromwell governed.                    --Swift.

   {Rump steak}, a beefsteak from the rump. --Goldsmith.

Source : WordNet®

rump
     n 1: the part of a quadruped that corresponds to the human
          buttocks [syn: {hindquarters}, {croup}, {croupe}]
     2: fleshy hindquarters; behind the loin and above the round
     3: the fleshy part of the human body that you sit on; "he
        deserves a good kick in the butt"; "are you going to sit
        on your fanny and do nothing?" [syn: {buttocks}, {nates},
        {arse}, {butt}, {backside}, {bum}, {buns}, {can}, {fundament},
         {hindquarters}, {hind end}, {keister}, {posterior}, {prat},
         {rear}, {rear end}, {stern}, {seat}, {tail}, {tail end},
        {tooshie}, {tush}, {bottom}, {behind}, {derriere}, {fanny},
         {ass}]