n. One who or that which rotates, or causes rotation; any rotational agency or instrument.n. Specifically, in anatomy, a muscle that produces a rolling or rotatory motion of a part; a muscle which rotates a part upon its own axis.n. In metal-working, a revolving or rotary furnace.n. In photometry, a mounting for an incandescent lamp so constructed that the lamp may be given a rapid rotation about its polar axis. By means of such a device the mean horizontal intensity of the lamp may be determined from a single photometric setting.n. In mathematics, a quantity having magnitude, direction, and position; a rotor.