Source : Webster's Revised Unabridged Dictionary (1913)

Hummer \Hum"mer\, n.
   1. One who, or that which, hums; one who applauds by humming.
      --Ainsworth.

   2. (Zo["o]l.) A humming bird.

Source : WordNet®

hummer
     n 1: a singer who produces a tune without opening the lips or
          forming words
     2: (baseball) a pitch thrown with maximum velocity; "he swung
        late on the fastball"; "he showed batters nothing but
        smoke" [syn: {fastball}, {heater}, {smoke}, {bullet}]