The Collaborative International Dictionary of English v.0.48:

accoutrement \accoutrement\ n.
   1. an item of clothing that is worn or carried, but not part
      of one's main clothing.

   Syn: accessory, accouterment
        [WordNet 1.5] Accouterments

WordNet (r) 3.0 (2006):

accoutrement
    n 1: clothing that is worn or carried, but not part of your main
         clothing [syn: accessory, accoutrement, accouterment]