A tooth on the rim of a wheel or gear that engages with a corresponding tooth on another wheel or gear to transmit motion. The cog in the machine was worn out, causing the entire system to malfunction.
A person who plays a minor but necessary role in a large organization or process. Even though he felt like just a cog in the corporate machine, his contributions were essential to the project's success.
A gearwheel; a wheel with projecting teeth that mesh with those of another wheel. The watchmaker carefully cleaned each tiny cog before reassembling the timepiece.
A round-hulled sailing vessel of the Middle Ages, used chiefly in northern European trade. The Hanseatic merchants transported their goods across the Baltic Sea in sturdy cogs.