Source : Webster's Revised Unabridged Dictionary (1913)

Crackajack \Crack"a*jack`\, n.
   1. An individual of marked ability or excellence, esp. in
      some sport; as, he is a crackajack at tennis. [Slang]

   2. A preparation of popped corn, candied and pressed into
      small cakes. [U. S.]

Crackajack \Crack"a*jack`\, a.
   Of marked ability or excellence. [Slang]