The Collaborative International Dictionary of English v.0.48:

Nutshell \Nut"shell`\, n.
   1. The shell or hard external covering in which the kernel of
      a nut is inclosed.
      [1913 Webster]

   2. Hence, a thing of little compass, or of little value.
      [1913 Webster]

   3. (Zool.) A shell of the genus Nucula.
      [1913 Webster]

   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]

WordNet (r) 3.0 (2006):

nutshell
    n 1: the shell around the kernel of a nut

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "nutshell":
   abridge, ace, atom, bit, brief, capsule, capsulize, condense, dab,
   digest, dole, dot, dram, dribble, driblet, dwarf, farthing, fleck,
   flyspeck, fragment, gobbet, grain, granule, groat, hair, handful,
   inventory, iota, jot, little, little bit, minim, minimum, minutiae,
   mite, modicum, molecule, mote, ounce, outline, particle, pebble,
   pinch, pittance, point, scruple, shorten, sketch, sketch out,
   smidgen, smitch, speck, spoonful, spot, sum, sum up, summarize,
   summate, synopsize, thimbleful, tiny bit, tittle, trifling amount,
   trivia, whit