in·​fil·​trate | \in-ˈfil-ˌtrāt, ˈin-(ˌ)fil- \
infiltrated; infiltrating

Definition of infiltrate 

transitive verb

1 : to cause (something, such as a liquid) to permeate something by penetrating its pores or interstices

2 : to pass into or through (a substance) by filtering or permeating

3 : to pass (troops) singly or in small groups through gaps in the enemy line

4 : to enter or become established in gradually or unobtrusively usually for subversive purposes the intelligence staff had been infiltrated by spies

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 \ noun
infiltrative \ ˈin-​(ˌ)fil-​ˌtrā-​tiv , in-​ˈfil-​trə-​ \ adjective
infiltrator \ in-​ˈfil-​ˌtrā-​tər , ˈin-​(ˌ)fil-​ \ noun

Synonyms for infiltrate


insinuate, slip, sneak, wind, work in, worm, wriggle

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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

Per last week's article, the company is alleged to have had its motherboards infiltrated by Chinese malware during the manufacturing process before their export to U.S. markets. Sam Blum, Popular Mechanics, "New Report Claims More Evidence of Chinese Microchip Tampering," 9 Oct. 2018 PiS’s pretext to reform the judiciary was that this branch of government remains infiltrated by members and collaborators of the former communist regime. Monika Nalepa, Washington Post, "Poland may forcibly ‘retire’ dozens of Supreme Court justices," 10 July 2018 Sewage backups usually happen during storms because water that permeates the soil is able to infiltrate the clay pipes and overwhelm the system, Kiefer said. Cody Boteler,, "Relief sewer construction in Academy Heights in the pipeline for November, county says," 10 July 2018 The military, in disarray, is easily infiltrated by the huckster Tobias Beckett and his gang, who pass themselves off as a captain and infantry. Amy Erica Smith, Vox, "Solo reveals the weakness of the Star Wars Galactic Empire," 20 June 2018 While the precise methods used by hacker activists are veiled in secrecy, Mr. Nimirovski said his team has used false digital identities to infiltrate hidden cybercrime sites to gather information on pedophiles. Inna Lazareva, The Christian Science Monitor, "Vigilante hackers work to save human trafficking victims," 20 June 2018 Costarring Adam Driver as the partner/frontman Washington used to infiltrate the group. Gary Thompson,, "Summer movies 2018: Here's when 'Ocean's 8,' 'Incredibles 2,' 'Jurassic World' and more hit theaters," 6 June 2018 The Chesapeake Bay region also has been infiltrated by nutria. Kurtis Alexander, San Francisco Chronicle, "Eradication of invasive rodent off to a slow start in California," 12 May 2018 What began as strictly functional tools made from local stone were gradually infiltrated by the occasional smaller tool and transported material. Lorraine Boissoneault, Smithsonian, "Colored Pigments and Complex Tools Suggest Humans Were Trading 100,000 Years Earlier Than Previously Believed," 16 Mar. 2018

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 1

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Last Updated

12 Nov 2018

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Time Traveler for infiltrate

The first known use of infiltrate was in 1758

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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, ˈin-(ˌ) \
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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full of whispering sounds

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