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
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
When HOXD13 was turned off, more T cells were able to infiltrate tumors.
From Science Daily ● Apr. 21, 2026
Which enables her to gain his confidence and infiltrate his closed world.
From The Wall Street Journal ● Apr. 9, 2026
In August 1925, White sent his undercover operatives to infiltrate the town of Ralston.
From "Killers of the Flower Moon" by David Grann
The Interior Ministry, with an estimated 140,000 state security officials and 500,000 informants, monitors and infiltrates dissident movements.
From The Wall Street Journal ● Jul. 5, 2026
Jonathan infiltrates Teddy’s organization, posing as a cavalier, rich businessman named Matthew Ellis.
From Los Angeles Times ● Jan. 11, 2026
"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
These deadly puzzles have already reeled in Holmes when the very American Amelia infiltrates 221B Baker Street, claiming to be his daughter.
From Salon ● Apr. 16, 2025
The blood which infiltrates the conjunctiva passes from behind forwards, appearing first at the outer angle of the eye and spreading like a fan towards the cornea.
From Manual of Surgery Volume Second: Extremities—Head—Neck. Sixth Edition. by Miles, Alexander
It admitted last week that its models broke out of their confined environment during testing, connected to the internet, and infiltrated Hugging Face, a site where developers store and share their code.
From Barron's ● Jul. 30, 2026
To time their strikes, they set up flags on infiltrated email systems so they see when payment-related messages land.
From The Wall Street Journal ● Jul. 21, 2026
During the investigation, NCA officers uncovered evidence that computer systems belonging to two US healthcare organisations, SSM Health and Sutter Health, had also been infiltrated and damaged.
From BBC ● Jun. 25, 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
The movement had been infiltrated with informers, and even well-intentioned people were generally not as tight-lipped as they should have been.
From "Long Walk to Freedom" by Nelson Mandela
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
Legacy food makers and buzzy upstarts are infiltrating households with many new condiments.
From The Wall Street Journal ● Apr. 17, 2026
There were stories in the paper of German parachutists disguised as nurses and nuns, spreading out through the cities and infiltrating the population.
From "Atonement" by Ian McEwan
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.
