ventilator

noun

1. a person or thing that ventilates.
2. a contrivance or opening for replacing foul or stagnant air with fresh air.
3. Medicine/Medical. a respirator.

noun

1. an opening or device, such as a fan, used to ventilate a room, building, etc
2. med a machine that maintains a flow of air into and out of the lungs of a patient who is unable to breathe normally