from
The Collaborative International Dictionary of English v.0.48
Servo-motor \Ser`vo-mo"tor\ (s[~e]r`v[-o]*m[=o]"t[~e]r), n.
[Sometimes erroneously spelt serro-motor.] [F. servo-moteur.
See {Serf}; {Motor}.]
1. (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.
[Webster 1913 Suppl.]
2. a motor which forms part of a {servomechanism}.
[PJC]