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 governor said state lawmakers during the 2021 session must take precautions against attempts by foreign governments, most notably China, to infiltrate agencies and universities to steal trade secrets. John Haughey, Washington Examiner, "Florida bills target Chinese ‘mass infiltration and theft of American research’," 3 Mar. 2021 King tells of William O’Neal (LaKeith Stanfield), an FBI informant assigned in the late 1960s to infiltrate the Illinois chapter of the Black Panther Party, led by the charismatic Fred Hampton (Daniel Kaluuya). Sean P. Means, The Salt Lake Tribune, "Here are 10 titles playing at the 2021 Sundance Film Festival likely to grab attention," 24 Jan. 2021 Even more insidiously, the Nazis worked to infiltrate crucial institutions like the police and the army. Benjamin Carter Hett, Star Tribune, "America has had its 'beer hall putsch'," 23 Jan. 2021 Under the late King Hassan II, Israeli intelligence agents were allowed to infiltrate an Arab League meeting in Casablanca in 1965, gaining insight that helped Israel to victory over Egypt, Jordan and Syria in the Six Day War the following year. Jared Malsin, WSJ, "Israel and Morocco Agree to Normalize Ties, Trump and Netanyahu Say," 10 Dec. 2020 In a way these infiltrate all the work shown here, as the combination of these events has so much influenced the way American readers in particular have experienced the year. Peter Van Agtmael, Magazine, "How photography helps us make sense of this unforgettable year," 8 Dec. 2020 By 1968, his assignment was simple–infiltrate the Illinois chapter of the Black Panther Party and get close to Fred Hampton. Zoe Guy, Marie Claire, "The True Story Behind 'Judas and the Black Messiah'," 12 Feb. 2021 Especially considering the way Wisconsin opened the season — Mertz threw five touchdowns in a near-perfect passing performance at Illinois — the storyline should be whether the Badgers can infiltrate the College Football Playoff race. Nathan Baird, cleveland, "Ohio State football’s Ryan Day on Wisconsin’s coronavirus cancellations: ‘You hold your breath all week’," 3 Nov. 2020 Court papers accused Ticketmaster of trying to infiltrate systems created by Songkick for artists that had hired the startup to help sell up to 10% of seats for U.S. tours directly through their fan clubs. Tom Hays,, "Ticketmaster to pay $10 million fine over hacking charges," 30 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

7 Mar 2021

Cite this Entry

“Infiltrate.” Dictionary, Merriam-Webster, Accessed 8 Mar. 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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