sentences:  First used c. 1300 in the sense of 'a wheel having teeth or cogs; late 14c., 'tooth on a wheel'; cog-wheel, early 15c.Historically, cogs were teeth made of wood rather than metal, and a cogwheel technically consisted of a series of wooden gear teeth located around a mortise (or mortice) wheel, each tooth forming a type of specialised 'through' mortise and tenon joint.The wheel can be made of wood, cast iron, or other material.