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 The poster job becomes an undercover mission to infiltrate a local organization; administrative work at a public park turns into a search operation for a man who has gone missing. Apoorva Tadepalli, The Atlantic, "The Paradox of Caring About ‘Bullshit’ Jobs," 2 Apr. 2021 Some variants with changes to their spike protein, which helps the virus infiltrate human cells, appear to partly elude the antibody response. Allysia Finley, WSJ, "Capitalism Is What Will Defeat Covid," 19 Mar. 2021 These sophisticated, sustained attacks are meant to infiltrate networks and conduct long-term operations, such as spying or data exfiltration. Roslyn Layton, Forbes, "Hackers Are Targeting U.S. Banks, And Hardware May Give Them An Open Door," 17 Mar. 2021 The attackers exploited a set of previously unknown bugs to infiltrate Exchange Server systems and target a range of the systems’ users. Robert Mcmillan, WSJ, "Suspected China Hack of Microsoft Shows Signs of Prior Reconnaissance," 7 Apr. 2021 One of Liddy's many imaginative suggestions was a proposal to send a team of ex-intelligence agents to infiltrate the offices of the Democratic National Committee in the Watergate in Washington and plant bugs on officials' telephones. Philip Terzian, Washington Examiner, "G. Gordon Liddy, 1930-2021," 1 Apr. 2021 To save his teenage son from an unjust prison sentence, a businessman makes a deal with a U.S. attorney to infiltrate a dangerous drug cartel and become an informant. Los Angeles Times, "Movies on TV this week: ‘Lust for Life’; ‘Platoon’ and more," 5 Mar. 2021 In the movie, a hero assembles a team to infiltrate the casino overrun by zombies. Janet W. Lee,, "Zack Snyder’s ‘Army of the Dead’ trailer plans a Las Vegas heist in a zombie apocalypse," 25 Feb. 2021 According to Marshall and Viganò, the progressive pontiff’s election culminates a centuries-long effort to infiltrate the Church with communism. Audrey Farley, The New Republic, "The Conservative War Against the Black Church," 21 Dec. 2020

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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Statistics for infiltrate

Last Updated

6 May 2021

Cite this Entry

“Infiltrate.” Dictionary, Merriam-Webster, Accessed 12 May. 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.
technical : 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

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