late 14c., "to fold, gather in pleats," also "to braid or weave," from Old French pleir "to fold," variant of ploier, ployer "to fold, bend," from Latin plicare "to fold" (see ply (v.1)). Related: Plaited; plaiting.
c.1400, "a fold, a crease," from Anglo-French pleit, Old French ploit, earlier pleit, "fold, manner of folding," from Latin plicatus, past participle of plicare "to lay, fold, twist" (see ply (v.1)). Meaning "interlaced strands of hair, ribbon, etc." is from 1520s, perhaps from plait (v.).