The Collaborative International Dictionary of English v.0.48:

Pleat \Pleat\ (pl[=e]t), n. & v. t.
   See Plait.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pleat
    n 1: 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: pleat or gather into a ruffle; "ruffle the curtain fabric"
         [syn: ruffle, pleat]
    2: fold into pleats, "Pleat the cloth" [syn: pleat, plicate]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "pleat":
   accordion pleat, aqueduct, box pleat, canal, canalization,
   canalize, carve, chamfer, channel, chisel, corrugate, crack,
   crease, crimp, crisp, cut, dado, dike, ditch, dog-ear, double,
   double over, enfold, engrave, entrenchment, flounce, flute, fold,
   fold over, fosse, frill, furrow, gash, gather, goffer, gouge,
   groove, gully, gutter, ha-ha, incise, infold, interfold, kennel,
   knife pleat, lap over, moat, plait, plat, plicate, plow, ply,
   quill, rabbet, rifle, ruff, ruffle, rut, score, scratch, slit,
   streak, striate, sunk fence, trench, trough, tuck, turn over,
   twill, wrinkle