\Co*coon"\, n. [F. cocon, dim. of coque shell of egge and
insects, fr. L. concha mussel shell. See {Conch}.]
1. An oblong case in which the silkworm lies in its chrysalis
   state. It is formed of threads of silk spun by the worm
   just before leaving the larval state. From these the silk
   of commerce is prepared.

2. (Zo["o]l.)
   (a) The case constructed by any insect to contain its
       larva or pupa.
   (b) The case of silk made by spiders to protect their
       eggs.
   (c) The egg cases of mucus, etc., made by leeches and
       other worms.