[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.
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.
  1. something that infiltrates.
  2. Pathology. any substance penetrating tissues or cells and forming a morbid accumulation.

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 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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
  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
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.

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.
  1. An abnormal substance that accumulates gradually in cells or body tissues.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.