filter

Concise Oxford English Dictionary © 2008 Oxford University Press:
filter/ˈfɪltə(r)/

▶noun

• 1 a porous device for removing impurities or solid particles from a liquid or gas passed through it.

  ■ a screen, plate, or layer which absorbs some of the light passing through it.

  ■ a device for suppressing electrical or sound waves of frequencies not required.

• 2 Brit. an arrangement whereby vehicles may turn left (or right) while other traffic waiting to go straight ahead or turn right (or left) is stopped by a red light.

• 3 Computing a piece of software that processes data before passing it to another application, for example to remove unwanted material.

▶verb

• 1 pass through a filter.

• 2 (often filter in/out/through) move or pass into something slowly or gradually.

  ■ (of information) gradually become known.

– derivatives
filterable (also filtrable) adjective.

– origin ME (denoting a piece of felt): from Fr. filtre, from med. L. filtrum ‘felt used as a filter’, of W. Gmc origin and rel. to felt1.