in·​fil·​trate | \ ˈin-(ˌ)fil- How to pronounce infiltrate (audio) , in-ˈfil-ˌtrāt How to pronounce infiltrate (audio) \
infiltrated; infiltrating

Definition of infiltrate

transitive verb

1 : to enter or become established in gradually or unobtrusively usually for subversive purposes the intelligence staff had been infiltrated by spies
2 : to pass (troops) singly or in small groups through gaps in the enemy line
3 : to pass into or through (a substance) by filtering or permeating
4 : to cause (something, such as a liquid) to permeate something by penetrating its pores or interstices

intransitive verb

: to enter, permeate, or pass through a substance or area by filtering or by insinuating gradually

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Other Words from infiltrate

infiltrate noun
infiltration \ ˌin-​(ˌ)fil-​ˈtrā-​shən How to pronounce infiltrate (audio) \ noun
infiltrative \ ˈin-​(ˌ)fil-​ˌtrā-​tiv How to pronounce infiltrate (audio) , in-​ˈfil-​trə-​ \ adjective
infiltrator \ ˈin-​(ˌ)fil-​ˌtrā-​tər How to pronounce infiltrate (audio) , in-​ˈfil-​ How to pronounce infiltrate (audio) \ noun

Synonyms for infiltrate


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Examples of infiltrate in a Sentence

The gang was infiltrated by undercover agents. Attempts to infiltrate undercover agents into the gang have failed. Water can easily infiltrate the soil.
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Recent Examples on the Web Such efforts have been simmering around the country for years, spurred by FBI reports starting more than 15 years ago that document a concerted effort by white supremacist and other extremist organizations to infiltrate the police., 11 May 2021 Also top notch is fellow Oscar nominee LaKeith Stanfield, who plays the small-time Chicago criminal recruited by the FBI to infiltrate Hampton's inner circle. USA Today, 22 Apr. 2021 Lawmakers in both chambers and from both parties vowed to find out how those responsible for Capitol security had allowed a violent mob to infiltrate the building. New York Times, 3 Aug. 2021 Past research has shown that this is the point of entry that allows the coronavirus to infiltrate the brain, which is why people commonly lose their sense of smell. NBC News, 29 July 2021 Here was statistical proof that their approach — a collaboration with the Indonesian government to infiltrate poaching networks and prevent a cycle of livestock deaths and revenge killings — had been effective. New York Times, 11 Aug. 2021 Mayra left her native Honduras in March with her two children, ages 2 and 6, after a hurricane last year wiped out her crops, ravaging her farming business; criminal organizations had also begun to infiltrate her neighborhood., 24 Apr. 2021 The Trump administration called him a terrorist and held him up as an example of how dangerous people were using the refugee resettlement program to infiltrate the United States. Washington Post, 30 July 2021 This year, however, Iran, Turkey, and Islamic terrorist organizations have intensified their efforts to openly infiltrate the minds of susceptible young Americans through the anti-Israel movement. Eitan Fischberger, National Review, 25 July 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'infiltrate.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of infiltrate

1758, in the meaning defined at transitive sense 4

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Time Traveler for infiltrate

Time Traveler

The first known use of infiltrate was in 1758

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Dictionary Entries Near infiltrate



infiltration capacity

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Statistics for infiltrate

Last Updated

27 Sep 2021

Cite this Entry

“Infiltrate.” Dictionary, Merriam-Webster, Accessed 27 Sep. 2021.

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More Definitions for infiltrate



English Language Learners Definition of infiltrate

: to secretly enter or join (something, such as a group or an organization) in order to get information or do harm
: to cause (someone) to secretly enter or join a group, organization, etc.
: to pass into or through (something)


in·​fil·​trate | \ in-ˈfil-ˌtrāt How to pronounce infiltrate (audio) , ˈin-(ˌ) How to pronounce infiltrate (audio) \
infiltrated; infiltrating

Medical Definition of infiltrate

 (Entry 1 of 2)

transitive verb

1 : to cause (as a liquid) to permeate something by penetrating its pores or interstices infiltrate tissue with a local anesthetic
2 : to pass into or through (a substance) by filtering or permeating

intransitive verb

: to enter, permeate, or pass through a substance or area



Medical Definition of infiltrate (Entry 2 of 2)

: something that passes or is caused to pass into or through something by permeating or filtering especially : a substance that passes into the bodily tissues and forms an abnormal accumulation a lung infiltrate

More from Merriam-Webster on infiltrate

Nglish: Translation of infiltrate for Spanish Speakers

Britannica English: Translation of infiltrate for Arabic Speakers


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