diffuser

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that diffuses, as.
• noun A light fixture, such as a frosted globe, that spreads light evenly.
• noun A medium that scatters light, used in photography to soften shadows.
• noun A device, such as a cone or baffle, placed in front of a loudspeaker diaphragm to diffuse the sound waves.
• noun A flow passage in a wind tunnel that decelerates a stream of gas or liquid from a high to a low velocity.

from The Century Dictionary.

• noun One who or that which diffuses; specifically, in physics, an apparatus consisting of a number of thin metal plates, designed to conduct away the heat of a thermoelectric battery by exposing a large surface to the air. Also spelled diffusor.
• noun In electricity, a reflector placed above an arc-lamp for the purpose of more uniformly distributing its light.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, diffuses.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any person or thing that diffuses
• noun A device designed to diffuse a scent efficiently
• noun optics Any device that or spreads out or scatters light, making the light appear softer
• noun automotive A shaped section of a car's underbody which improves the car's aerodynamic properties
• noun thermodynamics A mechanical device that is designed to control the characteristics of a fluid at the entrance to a thermodynamic open system
• noun sewage treatment An aerating device consisting of a membrane with fine pores, through which air is blown to generate small bubbles
• noun cooking A cooking item that can be placed above a stove heating element or burner to separate the cooking utensil from the heat source

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun baffle that distributes sound waves evenly
• noun optical device that distributes the light of a lamp evenly