- noun a muscle, gland or organ capable of responding to a nerve impulse
- noun a substance that controls protein synthesis by binding to an enzyme and increasing or decreasing its activity
- In robotics, a device which moves a component such, as a manipulator, in response to signals from the controller. Such a device may be electric, hydraulic, mechanical, or pneumatic. Also called actuator (3), or robotic actuator.
- noun a muscle movement or other bodily action that brings about a desired effect