The Collaborative International Dictionary of English v.0.48:

Horsehair \Horse"hair`\, n.
   A hair of a horse, especially one from the mane or tail; the
   hairs of the mane or tail taken collectively; Specifically: a
   black shiny fabric made of such hairs, used commonly in the
   1800's as a covering for stuffed furniture such as chairs and
   couches.
   [1913 Webster +PJC]

   Horsehair worm (Zool.), the hair worm or gordius.
      [1913 Webster]