Definition of "ply" []

• To join together, as by molding or twisting. (verb-transitive)
• To double over (cloth, for example). (verb-transitive)
• A layer, as of doubled-over cloth or of paperboard. (noun)
• One of the sheets of wood glued together to form plywood. (noun)
• A layer of rubber-coated fabric, often of nylon or polyester cords, forming the body of an automobile tire. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Above you see two skeins of Rowanspun 4-ply, which is discontinued."
• "There were a few lighters and barges, but none of the great merchant-men such as ply the upper air between the cities of the outer world."
• "If "ply" yarns are desired, 2 to 6 of the strands are twisted into a single cord, by special machinery managed by 5 or 6 men."