Originally: the motor areas of the brain (now rare); a hypothetical centre coordinating these (disused). Later also: the motor apparatus of the body; motor functioning or performance.
In some ciliate protozoans: an area of cytoplasm containing a system of fibrils connected with the cirri or myonemes, thought to be a centre of neuromotor control. Now chiefly historical.
Early 20th century; earliest use found in William Dorland (1864–1956), obstetrician. From scientific Latin motorium, use as noun of neuter of post-classical Latin motorius, in motorium commune.