1. To apply oneself diligently
2. To travel a route regularly; SYN. run.
3. To use diligently
4. To wield vigorously

ETYM Cf. French pli, from plier. Related to Ply.
1. One of the strands twisted together to make yarn or rope or thread; often used in combination: or.
2. Usually used in combination; one of several layers of cloth or paper or wood as in plywood.