Yes, ply is a Scrabble word!

Verb

1. Give what is desired or needed, especially support, food or sustenance

2. Apply oneself diligently

3. Travel a route regularly

4. Join together as by twisting, weaving, or molding

5. Wield vigorously

6. Use diligently

Noun

1. One of the strands twisted together to make yarn or rope or thread; often used in combination

2. (usually in combinations) one of several layers of cloth or paper or wood as in plywood