General English

  • noun a piece of equipment or material through which liquids or air can pass in order to remove any substances which are not wanted
  • noun a piece of glass on a camera which allows only certain colours or levels of light to pass through
  • noun material at the end of a cigarette, used to remove nicotine

General Science

  • noun an electric, electronic, acoustic, or optical device used to reject signals, vibrations, or radiation of specific frequencies while passing others


  • In optical astronomy, a device for selecting a wavelength of radiation, e.g. to allow only yellow light or only light of a particular spectral line to be observed. Optical filters can be made to allow light from a range of just a few Ångstroms to be passed, although this means losing almost all the light received, so that solar astronomers, who have lots of energy to play with, are the main users of these very narrow filters. In radio astronomy, filter effects are obtained by tuning receivers to record a wider or narrower range of radiation.


  • noun a material or device through which a liquid or a gas is passed in order to separate the fluid from solid matter or to remove unwanted substances
  • noun an electric, electronic, acoustic, or optical device used to reject signals, vibrations, or radiations of particular frequencies while passing others
  • verb to pass a liquid or gas through a filter in order to remove unwanted substances

Cars & Driving

  • noun a device for removing dirt or suspended particles in a liquid or in the air


  • noun a process of analysis applied to incoming information in order to identify any material that could be of interest to an organisation


  • noun an electronic circuit that allows certain frequencies to pass while stopping others
  • noun a pattern of binary digits used to select various bits from a binary word. A one in the filter retains that bit in the source word.
  • verb to remove unwanted elements from a signal or file
  • verb to select various records from a database file


  • A device to separate solids from air or liquids, such as a filter that removes dust from the air or impurities from water.
  • granular matter placed on an area to provide drainage while preventing the entry and flow of sediment and silt.


  • That which serves to selectively allow matter and/or energy to pass, remain, be blocked, or get absorbed.
  • An electric circuit or device which selectively transmits or rejects signals in one or more intervals of frequencies. The transmitted intervals are called passbands, and the rejected intervals are called stopbands. When a filter incorporates active components, such as transistors, it is an active filter, if not, it is passive. A capacitor, for instance, may serve as a passive filter, because it blocks DC. Filters may be classified as falling within one of the following four categories: low-pass, high-pass, bandpass, and bandstop. There are many examples of filters, including comb, ripple, Butter-worth, and loop filters. Also called electrical filter, or electrical-wave filter.
  • A device which blocks or absorbs sounds of certain frequencies while leaving others unaffected. Also called acoustic filter, or sound filter.
  • An element or device, such as a disk or plate of plastic or glass, which selectively blocks or absorbs one or more intervals of frequencies of electromagnetic radiation, such as light. The optical properties of the element or device determine which frequencies pass, and which are blocked or absorbed. Also called optical filter, or radiation filter (2).
  • In computers, a program, function, or process which transforms data from one format to another. For instance, such a filter may convert a document from the format of one word processing application to that of another.
  • In computers, a program, function, or process which selectively passes or separates data or items. For example, an email filter.


  • noun a piece of cloth, plastic or paper or a mass of crystals through which water or air passes and which holds back solid particles such as dirt
  • noun a piece of paper through which coffee passes in a coffee machine and which separates off the coffee grounds
  • verb to pass liquid through a paper or cloth filter, or through crystals, to remove impurities

Information & Library Science

  • verb to allow information to come out very gradually

Media Studies

  • noun a cover which is put over a light or camera lens to give a particular effect, e.g. a colour cast


  • noun a piece of paper or cloth through which a liquid is passed to remove any solid substances in it
  • verb to pass a liquid through a membrane, piece of paper or cloth to remove solid substances


  • noun a sheet of coloured glass or plastic, which stops certain frequencies of light and is used to make colour separations


  • to strain out any solids in a wine and clarify it just before it is bottled. The solids are mostly yeast cells and sediment that could spoil the wine.

Origin & History of “filter”

Ultimately, filter is the same word as felt – and indeed that is what it first meant in English (‘They dwell all in tents made of black filter’, John Mandeville, Travels 1400). It comes via Old French filtre from medieval Latin filtrum, which was borrowed from prehistoric west Germanic *filtiz, source of English felt. The modern sense of filter did not develop until the 17th century; it came from the use of felt for removing impurities from liquid. The derivative infiltrate dates from the 18th century. (The homophonic philtre (16th c.) is not related; it comes ultimately from Greek phílos ‘beloved’.).