to be in a nutshell

Nutshell \Nut"shell`\, n.
   1. The shell or hard external covering in which the kernel of
      a nut is inclosed.
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   2. Hence, a thing of little compass, or of little value.
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   3. (Zool.) A shell of the genus Nucula.
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   {in a nutshell} in a summarized and very abbreviated form; --
      of statments, descriptions, reports, and other
      communications; as, to describe the convention in a
      nutshell.

   {To be in a nutshell} or {To 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.
      [1913 Webster +PJC]