Mortise (?), n. [F. mortaise; cf. Sp. mortaja, Ar. murtazz fixed, or W. mortais, Ir. mortis, moirtis, Gael. moirteis.] A cavity cut into a piece of timber, or other material, to receive something (as the end of another piece) made to fit it, and called a tenon.
[1913 Webster]

Mortise and tenon (Carp.), made with a mortise and tenon; joined or united by means of a mortise and tenon; -- used adjectively. -- Mortise joint, a joint made by a mortise and tenon. -- Mortise lock. See under Lock. -- Mortise wheel, a cast-iron wheel, with wooden clogs inserted in mortises on its face or edge; -- also called mortise gear, and core gear.
[1913 Webster]