The Collaborative International Dictionary of English v.0.48:

eggshell \egg"shell`\, n.
   1. The shell or exterior covering of an egg. Also used
      figuratively for anything resembling an eggshell.
      [1913 Webster]

   2. (Zo["o]l.) A smooth, white, marine, gastropod shell of the
      genus Ovulum, resembling an egg in form.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

eggshell \egg"shell`\, a.
   1. of a pale, yellowish-white color; as, an eggshell ceiling
      and light green walls.
      [1913 Webster +PJC]

   2. (Architecture) having a smooth but not glossy texture like
      that of a hen's egg; as, a latex paint giving an eggshell
      finish. Also referred to as matte glaze or non-lustrous
      glaze.
      [PJC]

WordNet (r) 3.0 (2006):

eggshell
    n 1: the exterior covering of a bird's egg [syn: shell,
         eggshell]