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.
See Examples For:
"There was no one who moved without security knowing it, and that allowed us to infiltrate counter-revolutionary organizations," he said in 2018 in a rare interview with Cuban state TV.
From Barron's ● Jun. 23, 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
While seizing on a story about Manhattanites living in storage facilities, he meets Virginia, with whom he concocts a plan to infiltrate a massive Oklahoma data center.
From Los Angeles Times ● May 12, 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
"When corruption infiltrates the sport, it brings disgrace not only to the participants but damages the public trust in an institution that is vital and dear to all of us," Mr Nocella added.
From BBC ● Nov. 9, 2025
"When corruption infiltrates the sport, it brings disgrace not only to the participants but damages the public trust in an institution that is vital and dear to all of us."
From Barron's ● Nov. 9, 2025
Apple also recently postponed the on-the-news thriller series called “The Savant,” starring Jessica Chastain as an undercover investigator who infiltrates online hate groups, following the killing of Charlie Kirk.
From The Wall Street Journal ● Oct. 6, 2025
“Karlyn Borysenko infiltrates their meetings, collects their materials, decodes their language, and exposes their ideas,” reads her description of her Substack.
From Salon ● Sep. 23, 2025
The destruction cannot be prevented, for the water infiltrates through the soil; and some day, ere long, the remaining columns will be hurled down, and the pride of Karnac will lie prone in the dust.
From Roman Mosaics Or, Studies in Rome and Its Neighbourhood by Macmillan, Hugh
For the documentary, Davies teamed up with investigative journalist Liam Connell, who has previously infiltrated secretive online networks.
From BBC ● Jul. 13, 2026
He acknowledged that Russian troops have tried to seize the town and had infiltrated it in small groups.
From Barron's ● Jul. 4, 2026
Epstein’s network had infiltrated the boardrooms of hundreds of major U.S. companies, with clear consequences for corporate misconduct affecting employees and the broader business culture.
From Salon ● Jun. 20, 2026
Called Debug, the project targets Aedes aegypti mosquitoes, which are native to Africa but have infiltrated nearly half of California’s counties since first being detected in the state in 2013.
From Los Angeles Times ● Jun. 4, 2026
To completely ensure the men didn't double-cross the Nazi regime, they were warned that Gestapo agents had infiltrated the FBI.
From Nazi Saboteurs by Samantha Seiple
He admitted that small groups of Russian troops have been infiltrating the town but insisted that fighting was ongoing.
From Barron's ● Jul. 4, 2026
“They’re infiltrating, pretending they’re parents or they know people, but I’m the mom. I know who they are.”
From Los Angeles Times ● May 14, 2026
There it was, my recent cancer diagnosis, infiltrating my life again, via a spinach-pushing bot.
From Slate ● May 6, 2026
The one that Eddy, unbeknownst to her, is infiltrating.
From The Wall Street Journal ● Apr. 21, 2026
MK had been slowly infiltrating men back into the country with forged identity documents.
From "Long Walk to Freedom" by Nelson Mandela
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.
