A mortice is the cavity cut to hold a tenon. Because of the grain structure of wood, a mortice goes through the side of a timber, while a tenon is cut on the end. Tenon comes from the same root word as tendon, tenant, and tenacious, all in the sense of holding. A tenon is any extension that fits into a socket or mortice in another piece to help hold the two together. A tenon is usually a continuous part of one of the two pieces, but it may also be an independent part, or a "free" tenon. In this last sense, a dowel joining two boards is a free tenon.