filter

A device which separates a suspended, dissolved, or particulate matter from a fluid, solution, or other substance; any device that separates one substance from another.

Electronics or software that separates unwanted signals (for example noise) from wanted signals or that attenuates selected frequencies.

Any item, mechanism, device or procedure that acts to separate or isolate.

"He runs an email filter to catch the junk mail."

To sort, sift, or isolate.

"This strainer should filter out the large particles."

To diffuse; to cause to be less concentrated or focused.

"The leaves of the trees filtered the light."

To pass through a filter or to act as though passing through a filter.

"The water filtered through the rock and soil."