• synonyms


[in-fil-treyt, in-fil-treyt]
verb (used with object), in·fil·trat·ed, in·fil·trat·ing.
  1. to filter into or through; permeate.
  2. to cause to pass in by filtering.
  3. to move into (an organization, country, territory, or the like) surreptitiously and gradually, especially with hostile intent: The troops infiltrated the enemy lines.
  4. to pass a small number of (soldiers, spies, or the like) into a territory or organization clandestinely and with hostile or subversive intent: The intelligence agency infiltrated three spies into the neighboring country.
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verb (used without object), in·fil·trat·ed, in·fil·trat·ing.
  1. to pass into or through a substance, place, etc., by or as by filtering.
  2. Pathology. to penetrate tissue spaces or cells.
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  1. something that infiltrates.
  2. Pathology. any substance penetrating tissues or cells and forming a morbid accumulation.
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Origin of infiltrate

First recorded in 1750–60; in-2 + filtrate
Related formsin·fil·tra·tive [in-fil-trey-tiv, in-fil-truh-] /ˈɪn fɪlˌtreɪ tɪv, ɪnˈfɪl trə-/, adjectivein·fil·tra·tor [in-fil-trey-ter, in-fil-trey-] /ˈɪn fɪlˌtreɪ tər, ɪnˈfɪl treɪ-/, nounre·in·fil·trate, verb, re·in·fil·trat·ed, re·in·fil·trat·ing.un·in·fil·trat·ed, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for infiltrative


  1. to undergo or cause to undergo the process in which a fluid passes into the pores or interstices of a solid; permeate
  2. military to pass undetected through (an enemy-held line or position)
  3. to gain or cause to gain entrance or access surreptitiouslythey infiltrated the party structure
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  1. something that infiltrates
  2. pathol any substance that passes into and accumulates within cells, tissues, or organs
  3. pathol a local anaesthetic solution injected into the tissues to cause local anaesthesia
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Derived Formsinfiltration, nouninfiltrative, adjectiveinfiltrator, noun

Word Origin for infiltrate

C18: from in- ² + filtrate
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for infiltrative



1758, of fluids, from in- (2) "in" + filtrate. Related: Infiltrated; infiltrating. Military sense of "penetrate enemy lines" attested from 1934.

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Online Etymology Dictionary, © 2010 Douglas Harper

infiltrative in Medicine


(ĭn-fĭltrāt′, ĭnfĭl-)
  1. To cause a liquid to permeate a substance by passing through its interstices or pores.
  2. To permeate a porous substance with a liquid or gas.
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  1. An abnormal substance that accumulates gradually in cells or body tissues.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.