filter

plural filters

1. 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.

   Then add four drops of crocodile semen, and pass the mixture through a filter.

   1961, Harry E. Wedeck, Dictionary of Aphrodisiacs, New York: The Citadel Press, page 152

2. Electronics or software that separates unwanted signals (for example noise) from wanted signals or that attenuates selected frequencies.
3. Any item, mechanism, device, or procedure that acts to separate or isolate.

   He runs an email filter to catch the junk mail.

   1 more example

   In America alone, people spent $170 billion on “direct marketing”—junk mail of both the physical and electronic varieties—last year. Yet of those who received unsolicited adverts through the post, only 3% bought anything as a result. If the bumf arrived electronically, the take-up rate was 0.1%. And for online adverts the “conversion” into sales was a minuscule 0.01%. That means about $165 billion was spent not on drumming up business, but on annoying people, creating landfill and cluttering spam filters.

   2013 May 25, “No hiding place”, in The Economist, volume 407, number 8837, page 74

4. figurativelySelf-restraint in speech.

   He's got no filter, and he's always offending people as a result.

   1 more example

   These were women with enormous feelings and, almost always, no filter to mediate their expression of them.

   2026 January 30, Judy Berman, “Catherine O’Hara Portrayed the Vain and Delusional With a Radical Lack of Vanity”, in TIME, archived from the original on 01 Feb 2026

5. mathematicsA non-empty upper set (of a partially ordered set) which is closed under binary infima (a.k.a. meets).

   The collection of cofinite subsets of ℝ is a filter under inclusion: it includes the intersection of every pair of its members, and includes every superset of every cofinite set.

   1 more example

   If (1) the universal set (here, the set of natural numbers) were called a "large" set, (2) the superset of any "large" set were also a "large" set, and (3) the intersection of a pair of "large" sets were also a "large" set, then the set of all "large" sets would form a filter.

6. artsA translucent object placed in the light path of a camera to remove certain wavelengths (colors), or a computer program that simulates such an effect.
7. social mediaAn appearance-altering digital image effect.

   He don't need no filter posting pictures!

   2013, Patent Pending, “All-Star Hipster”, in Brighter

present singular third person filters · participle present filtering · participle past filtered · past filtered

1. transitiveTo sort, sift, or isolate.

   This strainer should filter out the large particles.

   3 more examples

   “You have probably never seen anything like this before, Mr. Toler. It is baleen, or if you prefer it, whalebone, taken from the mouth of the bowhead whale. It is used by the whale to filter its food.”

   1954, Alexander Alderson, chapter 5, in The Subtle Minotaur

   Receivers often incorporate digital equalisers to 'mop up' slight intersymbol interference after initial filtering at the receiver.

   1992, Chris C. Bissell, David A. Chapman, Digital signal transmission (2nd edition), Cambridge University Press, →ISBN, page 147

   But fans’ emotions are no longer filtered through ticket or album sales; they’re heard directly, constantly, at all hours, on all the platforms people visit to generate and extinguish bad feelings in a never-ending cycle.

   2022 October 25, Willy Staley, “The Try Guys and the Prison of Online Fame”, in The New York Times Magazine

   Synonyms: to filter out

2. transitiveTo diffuse; to cause to be less concentrated or focused.

   The leaves of the trees filtered the light.

3. intransitiveTo pass through a filter or to act as though passing through a filter.

   The water filtered through the rock and soil.

4. intransitiveTo move slowly or gradually; to come or go a few at a time.

   The crowd filtered into the theater.

5. intransitiveTo ride a motorcycle between lanes on a road

   I can skip past all the traffic on my bike by filtering.

6. derogatoryintransitiveslanglifestyleTo be discouraged where a connoisseur or hardcore fan would not.

   Most people get filtered by that episode.

plural Filters

1. A surname from German.