A Cog

1. A tooth on a gear.
2. A gear; a cogwheel.
3. An unimportant individual in a greater system.
4. (carpentry) A projection or tenon at the end of a beam designed to fit into a matching opening of another piece of wood to form a joint.
5. (mining) One of the rough pillars of stone or coal left to support the roof of a mine.
6. (historical) A ship of burden, or war with a round, bulky hull.
7. A small fishing boat.