` ::Definitions from Chambers 20th century dictionary 1972: Servo ``of a system in which the main mechanism is set in operation by a subsidiary mechanism and is able to develop a force greater than the force communicated to it``. Servo-mechanism ``a closed-cycle control system in which a small input power controls a larger output power in a strictly proportianate manner``. There is no mention of feedback. I would say that a servomechanism may, or may not, include feedback system.   `