filter

American  

[fil-ter] / ˈfɪl tər /

noun

• filters
  plural

1. any substance, as cloth, paper, porous porcelain, or a layer of charcoal or sand, through which liquid or gas is passed to remove suspended impurities or to recover solids.

2. any device, as a tank or tube, containing such a substance for filtering.

3. any of various analogous devices, as for removing dust from air or impurities from tobacco smoke, or for eliminating certain kinds of light rays.

4. something that works like a filter, as by removing, blocking, or separating out certain elements.

   Kids often talk without a filter. Events can be distorted through the filter of memory.

5. Informal. a filter-tipped cigarette or cigar.

6. Photography.

   1. a lens screen of dyed gelatin or glass placed on a camera for controlling the rendering of color or for diminishing the intensity of light.

   2. Digital Technology. a data manipulation function that changes the color or sharpness of a digital image or overlays an additive or special effect element.

      Use a sepia filter to give your photos that old-timey look.

7. Electronics, Physics. a circuit or device that passes certain frequencies and blocks others.

8. Mathematics. a collection of subsets of a topological space, having the properties that the intersection of two subsets in the collection is a subset in the collection and that any set containing a subset in the collection is in the collection.

9. Computers. an algorithm that categorizes, sorts, prioritizes, or blocks data through rule-based protocols.

   an email filter that deletes messages with subject words found commonly in spam.

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verb (used with object)

• filters,
  present (3rd person singular)
• filtered,
  past participle,  past
• filtering
  present participle

1. to remove by the action of a filter.

2. Computers. to subject (data) to an algorithmic filter.

   The search engine will filter your query results based on your location and user profile.

3. to act as a filter for; to slow or partially obstruct the passage of.

   The thick leaves filtered the sunlight.

4. to pass through or as through a filter.

verb (used without object)

• filters,
  present (3rd person singular)
• filtered,
  past participle,  past
• filtering
  present participle

1. to pass or slip through slowly, as through an obstruction or a filter.

   Enemy agents managed to filter into the embattled country.

   Synonyms:

   leak, trickle, seep, sift, penetrate

filter British  

/ ˈfɪltə /

noun

1. a porous substance, such as paper or sand, that allows fluid to pass but retains suspended solid particles: used to clean fluids or collect solid particles

2. any device containing such a porous substance for separating suspensions from fluids

3. any of various porous substances built into the mouth end of a cigarette or cigar for absorbing impurities such as tar

4. any electronic, optical, or acoustic device that blocks signals or radiations of certain frequencies while allowing others to pass See also band-pass filter

5. any transparent disc of gelatine or glass used to eliminate or reduce the intensity of given frequencies from the light leaving a lamp, entering a camera, etc

6. a traffic signal at a road junction consisting of a green arrow which when illuminated permits vehicles to turn either left or right when the main signals are red

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verb

1. (often foll by out) to remove or separate (suspended particles, wavelengths of radiation, etc) from (a liquid, gas, radiation, etc) by the action of a filter

2. (tr) to obtain by filtering

3. to pass (through a filter or something like a filter)

   dust filtered through the screen

4. (intr) to flow slowly; trickle

filter Scientific  

/ fĭl′tər /

1. A material that has very tiny holes and is used to separate out solid particles contained in a liquid or gas that is passed through it.

2. A device that allows signals with certain properties, such as signals lying in a certain frequency range, to pass while blocking the passage of others. For example, filters on photographic lenses allow only certain frequencies of light to enter the camera, while polarizing filters allow only light polarized along a given plane to pass. Radio tuners are filters that allow frequencies of only a narrow range to pass into an amplification circuit.

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filter Cultural  

1. A computer software program that selectively screens out incoming information.

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Discover More

Spam may be the target of a filter, or parents may use a filter designed to prevent their child's access to pornographic or violent Web pages.

Other Word Forms

Derived Forms

• filterer
  noun
• nonfilter
  noun
• prefilter
  noun
• overfilter
  verb (used with object)
• refilter
  verb (used with object)
• unfiltering
  adjective
• well-filtered
  adjective

Inflected Forms

Nouns

• filters
  plural

Participles

• filtering
  present
• filtered
  past

Conjugated Forms

Present

• filter
  simple
• filters
  simple
• have filtered
  perfect
• has filtered
  perfect
• am filtering
  progressive
• are filtering
  progressive
• is filtering
  progressive
• have been filtering
  perfect progressive
• has been filtering
  perfect progressive

Past

• filtered
  simple
• had filtered
  perfect
• was filtering
  progressive
• were filtering
  progressive
• had been filtering
  perfect progressive

Future

• will filter
  simple
• will have filtered
  perfect
• will be filtering
  progressive
• will have been filtering
  perfect progressive

Etymology

Origin of filter

First recorded in 1375–1425; late Middle English filtre, from Medieval Latin filtrum “felt, piece of felt used to strain liquids,” from Germanic; see origin at felt ²

Explanation

A machine or device that removes dangerous or unwanted materials from a substance passing through it is called a filter. A kitchen water filter makes the water safer to drink — and also taste better. Cars have many different filters, each of which takes impurities out of air, fuel, or water before it enters the car's engine. Most coffee makers require paper filters that allow brewed coffee to flow into the pot while leaving the coffee grounds behind. Filter is also a verb, meaning to strain or remove particular particles. The Medieval Latin root is filtrum, or "felt," which was used by early chemists to strain liquids, especially when purifying water.

Example Sentences

See Examples For:

filter filters filtered filtering

Higher prices for a barrel of oil take time to filter down to retail gas prices, but a look at the oil market’s “prompt spread” shows bigger gas bills look likely.

From MarketWatch ● Sep. 14, 2026

Surgeons attached the pig kidney to the blood vessels inside Tim Andrews' body so the organ could filter the blood.

From BBC ● Sep. 3, 2026

Wastewater treatment plants in the U.S. and Mexico filter some of the contaminants, but those facilities have failed over the past decade and released hundreds of millions of gallons of raw sewage into the river.

From Los Angeles Times ● Sep. 2, 2026

Its Coronagraph Instrument will block and filter the light from stars so astronomers can study exoplanets and disks around them.

From Science Daily ● Aug. 28, 2026

Jason scrambled backwards, not fast enough, but his ventus proved a useful filter.

From "Blood of Olympus" by Rick Riordan

Children’s products, water filters and power tools also compete on safety.

From The Wall Street Journal ● Sep. 16, 2026

"People will find new ways to have fake filters, and correct certain parts of their videos or pictures," she says.

From BBC ● Aug. 28, 2026

Roman's Coronagraphic Instrument will use masks, prisms, detectors, filters, and self-flexing mirrors to demonstrate technologies capable of suppressing starlight.

From Science Daily ● Aug. 28, 2026

It will gradually turn a reddish, copper color as sunlight bends and filters through the atmosphere to fall on the otherwise-obscured part of the moon.

From Los Angeles Times ● Aug. 26, 2026

Even people who have less restrictive filters and a good feel for numbers will note an increasingly large number of coincidences, due in large measure to the number and complexity of man-made conventions.

From "Innumeracy: Mathematical Illiteracy and Its Consequences" by John Allen Paulos

From there, medbeds filtered out to the rest of the secret-space-program community and to other alternative subcultures, including the New Age world.

From Slate ● Sep. 22, 2026

And instead of relying on the local soil, they would pot the plants in a material made from coconut fiber, with nutrients and filtered water provided via drip-irrigation technology.

From The Wall Street Journal ● Sep. 15, 2026

Chris Lofts, the site manager, said the waste was first filtered before having water added and being fed into a digester to create methane.

From BBC ● Aug. 27, 2026

Flores, whose only public comments had for months been filtered through his legal team, agreed to speak with The Times, detailing the toll that the prior year and a half had taken on him.

From Los Angeles Times ● Aug. 26, 2026

The curtains were still open, and the only light in the room came from the moonlight filtered in through the window.

From "Ophie's Ghosts" by Justina Ireland

“So you get this sort of idea of a filtering through the supply chain, a filtering into other areas of the economy that would broaden the base of expansion.”

From The Wall Street Journal ● Sep. 25, 2026

I realized I was nervous and not filtering my words very well.

From Los Angeles Times ● Sep. 18, 2026

Yet when it comes to the ways AI is filtering into Americans’ jobs, many workers are looking at a trickle so far, rather than a flood.

From MarketWatch ● Sep. 1, 2026

This prominence emitted strongly in light associated with hydrogen, allowing its original bright pink color to survive despite the atmospheric filtering.

From Science Daily ● Aug. 20, 2026

I liked the stained glass in the sanctuary, even though crucified Jesus was really bloody, too bloody for stained glass, I thought, all those red and magenta pieces filtering sunlight.

From "The Miseducation of Cameron Post" by emily m. danforth

Related Words

• clean
• drain
• dribble
• leak
• penetrate
• percolate
• permeate
• refine
• sift
• trickle
• winnow