Real Dictionary

-ply
You use -ply after a number to indicate how many pieces are twisted together to make a type of wool, thread, or rope.

ply
verb: If you ply someone with food or drink, you keep giving them more of it.

ply in American English 1
to do work with; wield or use (a tool, faculty, etc.), esp. with energy
intransitive verb: to run or travel regularly over a fixed course or between certain places, as a boat, bus, etc
transitive verb: to work with or at diligently; employ busily; use

ply in American English 2
a single thickness, fold, or layer, as of doubled cloth, plywood, etc.
having (a specified number of) layers, thicknesses, or strands
to bend or submit
to bend, twist, fold, or mold
intransitive verb: to bend, incline, or yield
noun: a thickness or layer
transitive verb: to bend, fold, or mold

ply in British English 1
verb: to carry on, pursue, or work at (a job, trade, etc)

ply in British English 2
to twist together (two or more single strands) to make yarn
noun: a layer, fold, or thickness, as of cloth, wood, yarn, etc