From 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]
From 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. [1913 Webster]
2. A braid, as of hair or straw; a plat. [1913 Webster]
Polish plait. (Med.) Same as Plica. [1913 Webster]