The Collaborative International Dictionary of English v.0.48:

Vestment \Vest"ment\, n. [OE. vestement, vestiment, OF.
   vestement, vestiment, F. v[^e]tement, fr. L. vestimentum, fr.
   vestire to clothe, fr. vestis a garment, clothing. See
   Vest.]
   A covering or garment; some part of clothing or dress;
   specifically (Eccl.), any priestly garment. "Royal
   vestiment." --Chaucer. "Priests in holy vestments." --Shak.
   [1913 Webster]

         The sculptor could not give vestments suitable to the
         quality of the persons represented.      --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vestment
    n 1: gown (especially ceremonial garments) worn by the clergy

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "vestment":
   apparel, array, attire, bedizenment, blanket, canonicals,
   ceremonial attire, clericals, cloak, cloth, clothes, clothing,
   coat, costume, cover, coverage, covering, covert, coverture, cowl,
   cowling, curtain, drape, drapery, dress, dressing, duds,
   episcopal vestments, fashion, fatigues, feathers, fig, frock, garb,
   garment, garments, gear, gown, guise, habiliment, habit, hanging,
   hood, housing, investiture, investment, linen, liturgical garments,
   mantle, mask, pall, pontificalia, pontificals, rag, rags, raiment,
   robe, robes, screen, shelter, shield, shroud, sportswear, style,
   threads, togs, toilette, trim, veil, vestments, vesture, wear,
   wearing apparel