Source : Webster's Revised Unabridged Dictionary (1913)

Bumper \Bum"per\, n. [A corruption of bumbard, bombard, a large
   drinking vessel.]
   1. A cup or glass filled to the brim, or till the liquor runs
      over, particularly in drinking a health or toast.

            He frothed his bumpers to the brim.   --Tennyson.

   2. A covered house at a theater, etc., in honor of some
      favorite performer. [Cant]

Bumper \Bump"er\, n.
   1. That which bumps or causes a bump.

   2. Anything which resists or deadens a bump or shock; a
      buffer.

Source : WordNet®

bumper
     adj : extraordinarily abundant; "a bumper crop"

bumper
     n 1: a glass filled to the brim (especially as a toast); "we
          quaffed a bumper of ale"
     2: a mechanical device consisting of bars at either end of a
        vehicle to absorb shock and prevent serious damage