# filter

Pronunciation: US say "FIL-tur" /ˈfɪltɚ/; UK say "FIL-tuh" /ˈfɪltə/

## Noun

1. A device that separates suspended, dissolved, or particulate matter from a fluid or other substance; broadly, anything that separates one substance from another.
   - Simple: A device that removes unwanted bits from a liquid or gas as it passes through.
   - _The oil filter prevents debris from circulating through the engine._
   - _Municipal plants use sand filters to remove sediment before treating the water._
3. A digital image effect applied to a photo or video to alter its appearance.
   - Simple: A digital effect that changes how a photo or video looks, often on social media.
   - _The app's newest filter smooths skin and warms the lighting automatically._
   - _Influencers often swap filters until the mood of a post feels right._
4. Electronics or software that separates unwanted signals, such as noise, from wanted ones, or that weakens selected frequencies.
   - Simple: A part of a device that blocks unwanted signals or sounds and lets the wanted ones through.
   - _The engineer added a low-pass filter to remove high-frequency noise from the audio._
   - _Digital filters in the receiver isolate the desired channel from neighboring frequencies._
5. A translucent object placed in a camera's light path to remove certain wavelengths, or a program that simulates the same effect.
   - Simple: A clear or colored piece placed in front of a camera lens to block some light or colors.
   - _A polarizing filter cut the glare off the lake's surface._
   - _Landscape photographers stack neutral-density filters for long daytime exposures._
7. Self-restraint that keeps a person from blurting out blunt or inappropriate remarks.
   - Simple: The good sense to hold back rude or hurtful words before saying them.
   - _After a few drinks, his filter disappeared entirely._
   - _She admires people who speak with a filter and never wound others carelessly._
9. Anything, whether a physical device or a process, that serves to separate one thing from another or to screen some out.
   - Simple: Anything that works to separate or keep apart, whether an object or a method.
   - _A careful screening process can be a filter for unsuitable products._
   - _Tradition often works as a filter, isolating the practices a community wants to keep._
12. In order theory, a nonempty subset of a partially ordered set that is upward closed and contains the meet of any two of its elements.
   - Simple: In math, a special kind of group of elements chosen from an ordered set, following certain rules about which elements belong.
   - _A filter on a lattice must be closed under finite meets._
   - _Ultrafilters are maximal filters used heavily in set theory and topology._

## Verb

2. To sort, sift, or isolate items, keeping some and setting others aside.
   - Simple: To go through a group of things and keep only the ones you want.
   - _The software filters incoming messages by sender and subject._
   - _Reviewers filter thousands of submissions down to a handful of finalists._
6. To pass through a filter, or to move as if passing through one.
   - Simple: To move slowly through a material that holds part of it back.
   - _Moonlight filtered through the gaps in the old roof._
   - _Faint music seemed to filter up from the apartment below._
8. To pass from one place to another gradually or in small numbers.
   - Simple: To move somewhere slowly, a few people at a time.
   - _Commuters filtered onto the platform as the announcement played._
   - _News of the result began to filter through the crowd._
10. To diffuse something, making it less concentrated or less sharply focused.
   - Simple: To spread something out so it becomes weaker or less focused.
   - _Sheer drapes filter the daylight into a gentle glow._
   - _The canopy of leaves filtered the afternoon sun across the path._
11. To ride a motorcycle between lanes of slower or stationary traffic.
   - Simple: To ride a motorcycle forward between lines of slow or stopped cars.
   - _Riders are allowed to filter through congestion on many British roads._
   - _She filtered up to the lights while the cars waited._
13. To become discouraged and give up where a connoisseur or dedicated fan would not. *(slang)*
   - Simple: To quit or lose interest in something that a true fan would gladly keep enjoying.
   - _Newcomers often filter early in the series, missing its slow-burn payoff._
   - _Plenty of viewers filtered at the subtitled scenes, but die-hards stayed glued._

## Origin

From Middle English "filtre", from Medieval Latin "filtrum" (compare Old French "feutre", meaning felt or filter), which came from Frankish "*filtir" and Proto-West Germanic "*felt". It is related to the word "felt".

Source: DictionaryAI, https://dictionaryai.com/define/filter (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).