The Collaborative International Dictionary of English v.0.48:

Antimacassar \An`ti*ma*cas"sar\
   ([a^]n`t[i^]*m[.a]*k[a^]s"s[~e]r), n.
   A cover for the back or arms of a chair or sofa, etc., to
   prevent them from wear or from being soiled by macassar or
   other oil from the hair.
   [1913 Webster]

WordNet (r) 3.0 (2006):

antimacassar
    n 1: a piece of ornamented cloth that protects the back of a
         chair from hair oils