The Collaborative International Dictionary of English v.0.48:

Miniver \Min"i*ver\, n. [See Meniver.]
   A fur esteemed in the Middle Ages as a part of costume. It is
   uncertain whether it was the fur of one animal only or of
   different animals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

miniver
    n 1: trimming on ceremonial robes consisting of white or light
         grey fur