infiltrate
Americanverb (used with object)
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to filter into or through; permeate.
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to cause to pass in by filtering.
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to move into (an organization, country, territory, or the like) surreptitiously and gradually, especially with hostile intent.
The troops infiltrated the enemy lines.
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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)
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to pass into or through a substance, place, etc., by or as by filtering.
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Pathology. to penetrate tissue spaces or cells.
noun
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something that infiltrates.
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Pathology. any substance penetrating tissues or cells and forming a morbid accumulation.
verb
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to undergo or cause to undergo the process in which a fluid passes into the pores or interstices of a solid; permeate
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military to pass undetected through (an enemy-held line or position)
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to gain or cause to gain entrance or access surreptitiously
they infiltrated the party structure
noun
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something that infiltrates
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pathol any substance that passes into and accumulates within cells, tissues, or organs
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pathol a local anaesthetic solution injected into the tissues to cause local anaesthesia
Other Word Forms
Derived Forms
Inflected Forms
Participles
Conjugated Forms
Present
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infiltratesimple
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infiltratessimple
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have infiltratedperfect
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has infiltratedperfect
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am infiltratingprogressive
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are infiltratingprogressive
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is infiltratingprogressive
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have been infiltratingperfect progressive
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has been infiltratingperfect progressive
Past
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infiltratedsimple
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had infiltratedperfect
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was infiltratingprogressive
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were infiltratingprogressive
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had been infiltratingperfect progressive
Future
Etymology
Origin of infiltrate
Explanation
If you infiltrate a group or organization, you join it in order to gain information, like an employee of a donut shop that infiltrates the competition to try to learn its "secret recipe" for its delicious dough. Infiltrate is a verb that is familiar to international spies and undercover agents, who are all adept at joining a group under false pretenses, fitting in, and working their way up to the highest ranks in order to find out as much information as they can about the group. The word can be used more broadly to describe anything that stealthily becomes a part of something else, such as slang words that infiltrate our everyday speech.
Vocabulary lists containing infiltrate
A Separate Peace
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Vocabulary: A Rapper's Delight!
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While the World Watched
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
The army has been sending in small groups of soldiers to infiltrate and secure positions, a method previously used to capture the Ukrainian city of Pokrovsk in late 2025.
From Barron's • Jul. 4, 2026
Before the performers infiltrate the ship, “I’m trying to intentionally set up audience expectations to think they’re going to get this run-of-the-mill Hollywood death tour,” he explained.
From Los Angeles Times • Jun. 22, 2026
It recently arrested Iranian paramilitary troops it said were trying to infiltrate the country by sea and on Wednesday expelled two Iranian diplomats in response to the strikes.
From The Wall Street Journal • Jun. 4, 2026
A new wave of settlers – pastoralist-farmers hailing ultimately from the Russian steppe – began to infiltrate the Rhine area in the form of the Corded Ware culture.
From Science Daily • May 30, 2026
To infiltrate the impenetrable Ice Court and snatch a prize from the bastion of Fjerdan nobility and military might?
From "Six of Crows" by Leigh Bardugo
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
