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[fil-ter] /ˈfɪl tər/
Informal. a filter-tipped cigarette or cigar.
Photography. a lens screen of dyed gelatin or glass for controlling the rendering of color or for diminishing the intensity of light.
Electronics, Physics. a circuit or device that passes certain frequencies and blocks others.
verb (used with object)
to remove by the action of a filter.
The thick leaves filtered the sunlight.
to pass through or as through a filter.
verb (used without object)
Enemy agents managed to filter into the embattled country.
late Middle English
1375-1425; late Middle English filtre < Medieval Latin filtrum felt, piece of felt used to strain liquids < Germanic; see felt2
Related forms
filterer, noun
nonfilter, noun
overfilter, verb (used with object)
prefilter, noun
refilter, verb (used with object)
unfiltering, adjective
well-filtered, adjective
11. penetrate, sift, seep, trickle, leak. Unabridged
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British Dictionary definitions for prefilter


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
any device containing such a porous substance for separating suspensions from fluids
any of various porous substances built into the mouth end of a cigarette or cigar for absorbing impurities such as tar
any electronic, optical, or acoustic device that blocks signals or radiations of certain frequencies while allowing others to pass See also band-pass filter
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
(Brit) 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
(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
(transitive) to obtain by filtering
(intransitive) foll by through. to pass (through a filter or something like a filter): dust filtered through the screen
(intransitive) to flow slowly; trickle
Word Origin
C16 filtre from Medieval Latin filtrum piece of felt used as a filter, of Germanic origin; see felt²
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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Word Origin and History for prefilter



early 15c., from Old French filtre and directly from Medieval Latin filtrum "felt," which was used to strain impurities from liquid, from West Germanic *filtiz (see felt (n.)). Of cigarettes, from 1908.


1570s, from Medieval Latin filtrare, from filtrum (see filter (n.)). The figurative sense is from 1830. Related: Filtered; filtering.

Online Etymology Dictionary, © 2010 Douglas Harper
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prefilter in Medicine

filter fil·ter (fĭl'tər)


  2. A device containing such a substance.

  3. Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiations of certain frequencies while passing others.

  4. A translucent screen, used in both diagnostic and therapeutic radiology, that permits the passage of rays having desirable levels of energy.

  5. A device used in spectrophotometric analysis to isolate a segment of the spectrum.

v. fil·tered, fil·ter·ing, fil·ters
  1. To pass a liquid or gas through a filter.

  2. To remove by passing through a filter.

  3. To pass through or as if through a filter.

fil'ter·er n.
fil'ter·less adj.
The American Heritage® Stedman's Medical Dictionary
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prefilter in Science


The American Heritage® Science Dictionary
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prefilter in Culture

filter definition

A computer software program that selectively screens out incoming information.

Note: 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.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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