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]