Merriam-Webster's Collegiate® Dictionary, 11th Edition
PLY
I. verb (plied; plying)
Etymology: Middle English plien, short for applien to apply
Date: 14th century
transitive verb
1. to use or wield diligently , to practice or perform diligently , to keep furnishing or supplying something to ,
3. to make a practice of rowing or sailing over or on , to go or travel regularly over, on, or through , intransitive verb to apply oneself steadily, to go or travel regularly,
II. noun (plural plies)
Etymology: 3ply
Date: 1532
1. one of several layers (as of cloth) usually sewn or laminated together, one of the strands in a yarn, one of the veneer sheets forming plywood, a layer of a paper or cardboard, inclination , bias ,
III. transitive verb (plied; plying)
Etymology: Middle English plien to fold, from Anglo-French plier, pleier, from Latin plicare; akin to Old High German flehtan to braid, Latin plectere, Greek plekein
Date: circa 1909
to twist together