From WordNet (r) 3.0 (2006) [wn]:
diffuser
n 1: baffle that distributes sound waves evenly [syn:
diffuser, diffusor]
2: optical device that distributes the light of a lamp evenly
[syn: diffuser, diffusor]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Diffuser \Dif*fus"er\, n.
One who, or that which, diffuses.
[1913 Webster]