Source : Webster's Revised Unabridged Dictionary (1913)

Nutshell \Nut"shell`\, n.
   1. The shell or hard external covering in which the kernel of
      a nut is inclosed.

   2. Hence, a thing of little compass, or of little value.

   3. (Zo["o]l.) A shell of the genus Nucula.

   {To} {be, or lie}, {in a nutshell}, to be within a small
      compass; to admit of very brief or simple determination or
      statement. ``The remedy lay in a nutshell.'' --Macaulay.

Source : WordNet®

nutshell
     n : the shell around the kernel of a nut