one of the strands twisted together to make yarn or rope or thread; often used in combination
"three-ply cord"
"four-ply yarn"
(usually in combinations) one of several layers of cloth or paper or wood as in plywood
"The craftsman carefully stacked three thin sheets of birch veneer to create a single ply for the new tabletop."
A layer of material.
"The old boat was too heavy to change its course and could not ply in any other direction during the storm."
A bent; a direction.
To bend; to fold; to mould; (figuratively) to adapt, to modify; to change (a person's) mind, to cause (a person) to submit.
"The artist spent hours plying her craft to create a masterpiece worthy of display."
To work at (something) diligently.
The word "ply" comes from Middle English and French words meaning a fold or pleat. Its ultimate origin is an ancient root that meant to bend, fold, or plait.