The Collaborative International Dictionary of English v.0.48:

Pleach \Pleach\, v. t. [imp. & p. p. Pleached; p. pr. & vb. n.
   Pleaching.] [Cf. OF. plaissier to bend, and also F. plisser
   to plait, L. plicare, plicitum, to fold, lay, or wind
   together. Cf. Plash to pleach.]
   To unite by interweaving, as branches of trees; to plash; to
   interlock. "The pleached bower." --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pleach
    v 1: form or weave into a braid or braids; "braid hair" [syn:
         braid, pleach] [ant: unbraid]
    2: interlace the shoots of; "pleach a hedge" [syn: pleach,
       plash]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "pleach":
   braid, enlace, entwine, interknit, interlace, intertie,
   intertissue, intertwine, intertwist, interweave, intort, knit,
   lace, loom, loop, mat, net, noose, plait, raddle, splice, tissue,
   twill, twine, twist, wattle, weave, web, wreathe