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:
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
"These individuals risked their lives to infiltrate and inform on the activities of our nation's most radical and violent extremist groups," he said.
From BBC ● Apr. 22, 2026
When HOXD13 was turned off, more T cells were able to infiltrate tumors.
From Science Daily ● Apr. 21, 2026
Together, they can infiltrate the minds of good men and decide a battle before it's begun.
From "An Ember in the Ashes" by Sabaa Tahir
The stakes around AI are rising as it infiltrates every aspect of the economy.
From Los Angeles Times ● Mar. 5, 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," 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
The whole scheme of evolution infiltrates into the regular chela’s mind, by reason of the fact that he is made to see the process taking place by clairvoyant vision.
From Fashionable Philosophy and Other Sketches by Oliphant, Laurence
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
He acknowledged that Russian troops have tried to seize the town and had infiltrated it in small groups.
From Barron's ● Jul. 4, 2026
It was set up after senior police officer Lt-Gen Nhlanhla Mkhwanazi alleged last July that organised crime groups had infiltrated the government.
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
Either Tally infiltrated the Smoke and betrayed Shay, or she’d be an ugly for life.
From "Uglies" by Scott Westerfeld
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
In Jihad in America, Emerson used hidden-camera footage to try to build a case that jihadists were infiltrating Middle America.
From Slate ● Apr. 19, 2026
Legacy food makers and buzzy upstarts are infiltrating households with many new condiments.
From The Wall Street Journal ● Apr. 17, 2026
For weeks they had been silently infiltrating South Vietnam, and they struck with a coordinated fury that shocked everyone.
From "Boots on the Ground: America's War in Vietnam" by Elizabeth Partridge
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.
