Ply
A strand of yarn; yarn made of two or more strands twisted together is called two-ply or three-ply and is stronger and more even.
Also: two-ply, plied yarn
Ply is the number of single strands twisted together to make a thicker yarn. A two-ply yarn has two strands, a three-ply has three. Plying makes the yarn stronger and more regular, because thin places in one strand are covered by another, and it can balance the twist so that the yarn does not curl. Warp threads, which take the most strain on the loom, are often plied. Weavers and spinners use the word, and a label may say two-ply cotton or two-ply silk.