The Collaborative International Dictionary of English v.0.48:

Wig \Wig\, n. [Abbreviation from periwig.]
   [1913 Webster]
   1. A covering for the head, consisting of hair interwoven or
      united by a kind of network, either in imitation of the
      natural growth, or in abundant and flowing curls, worn to
      supply a deficiency of natural hair, or for ornament, or
      according to traditional usage, as a part of an official
      or professional dress, the latter especially in England by
      judges and barristers.
      [1913 Webster]

   2. An old seal; -- so called by fishermen.
      [1913 Webster]

   Wig tree. (Bot.) See Smoke tree, under Smoke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

wig tree
    n 1: Old World shrub having large plumes of yellowish feathery
         flowers resembling puffs of smoke [syn: Venetian sumac,
         wig tree, Cotinus coggygria]