What does nebulizer mean? nebulizer. Noun 1. A device used to convert liquid into a fine spray of aerosols, by means of oxygen, compressed air, or ultrasonic vibration; sometimes also referred to as an atomizer. 2. (medicine) ; A device used to administer a medicine into the lungs, by converting the medicine from liquid state into a fine spray of aerosols, to be inhaled through the nose or mouth. The conversion of liquid medicine is performed by means of oxygen or compressed air or ultrasonic vibration, which differ from the aerosolizing means used by inhalers and vaporizers.