Dictionary:

diffuser

  (dĭ-fyū'zər)

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

1. In production, screen used as a filter and placed over a light to soften the light and eliminate harsh tones or shadows.

2. Screen used over a camera lens to give the image a kind of fuzzy effect, as in a dream.

1. Any device, object, or surface that scatters light (or sound) from a source.
2. For air-conditioning systems, see air diffuser.

The noun has 2 meanings:

Meaning #1: baffle that distributes sound waves evenly
  Synonym: diffusor

Meaning #2: optical device that distributes the light of a lamp evenly
  Synonym: diffusor