To ply means to work at something steadily and diligently. A blacksmith plies her trade at the forge, hammering hot metal day after day. A baker plies his craft every morning, kneading dough and shaping loaves. When someone plies their trade, they're practicing their skill or profession with focus and dedication.

The word often appears in old-fashioned phrases about craftspeople and their work, but it applies to anyone who does something regularly and seriously. A musician might ply her instrument for hours each day, while a writer plies his pen (or keyboard), working on stories.

Ply also means to travel back and forth along a regular route. Ferries ply the waters between two islands, making the same journey repeatedly. In older times, merchant ships would ply trade routes across the ocean, carrying goods from port to port.

Finally, ply can mean to supply someone with something persistently. If you ply someone with questions, you keep asking them one after another. A host might ply guests with snacks and drinks, offering them repeatedly throughout a party.