The Collaborative International Dictionary of English v.0.48:

Plait \Plait\, v. t. [imp. & p. p. Plaited; p. pr. & vb. n.
   Plaiting.]
   1. To fold; to double in narrow folds; to pleat; as, to plait
      a ruffle.
      [1913 Webster]

   2. To interweave the strands or locks of; to braid; to plat;
      as, to plait hair; to plait rope.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plait \Plait\, n. [OE. playte, OF. pleit, L. plicatum, plicitum,
   p. p. of plicare to fold, akin to plectere to plait. See
   Ply, and cf. Plat to weave, Pleat, Plight fold.]
   1. A flat fold; a doubling, as of cloth; a pleat; as, a box
      plait.
      [1913 Webster]

            The plaits and foldings of the drapery. --Addison.
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   2. A braid, as of hair or straw; a plat.
      [1913 Webster]

   Polish plait. (Med.) Same as Plica.
      [1913 Webster]

WordNet (r) 3.0 (2006):

plait
    n 1: a hairdo formed by braiding or twisting the hair [syn:
         braid, plait, tress, twist]
    2: any of various types of fold formed by doubling fabric back
       upon itself and then pressing or stitching into shape [syn:
       pleat, plait]
    v 1: make by braiding or interlacing; "lace a tablecloth" [syn:
         braid, lace, plait]
    2: weave into plaits; "plait hair"