\Ser`vo-mo"tor\, n. [Sometimes erroneously spelt
serro-motor.] [F. servo-moteur. See {Serf}; {Motor}.] (Mach.)
A relay apparatus; specif.:
(a) An auxiliary motor, regulated by a hand lever, for
    quickly and easily moving the reversing gear of a large
    marine engine into any desired position indicated by that
    of the hand lever, which controls the valve of the motor.
(b) In a Whitehead torpedo, a compressed-air motor, for
    moving the rudders so as to correct deviations from the
    course.