ply one's trade

:  to use or wield diligently

:  to practice or perform diligently

:  to keep furnishing or supplying something to

:  one of several layers (as of cloth) usually sewn or laminated together

:  one of the strands in a yarn

:  one of the veneer sheets forming plywood

:  to twist together

:  the business of buying and selling or bartering commodities :  commerce

:  business, market

:  dealings between persons or groups

:  to give one thing in exchange for another

:  to engage in the exchange, purchase, or sale of goods

:  to make one's purchases :  shop

:  of, relating to, or used in trade

:  intended for or limited to persons in a business or industry

:  serving others in the same business rather than the ultimate user or consumer