a wheel or bar with a series of projections on its edge, which transfers motion by engaging with projections on another wheel or bar:the cogs and springs of a watch
each of the projections on a cog:applewood was the favourite material for the cogs or teeth of a cogwheel
a cog in the (or a) machine (or wheel)
a small or insignificant member of a larger organization or system:copywriters have been seen as just a cog in the big advertising machine
