What does "wrist" mean?

Wrist: (Mach.) A stud or pin which forms a journal; -- also called wrist pin. Bridle wrist, the wrist of the left hand, in which a horseman holds the bridle. -- Wrist clonus. Etym: [NL. clonus, fr. Gr. Clonic.] (Med.) A series of quickly alternating movements of flexion and extension of the wrist, produced in some cases of nervous disease by suddenly bending the hand back upon the forearm. -- Wrist drop (Med.), paralysis of the extensor muscles of the hand, affecting the hand so that when an attempt is made to hold it out in line with the forearm with the palm down, the hand drops. It is chiefly due to plumbism. Called also hand drop. -- Wrist plate (Steam Engine), a swinging plate bearing two or more wrists, for operating the valves.