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

Last winter, deicing fluid infiltrated some of the antennas and disrupted Wi-Fi service on board. Ally Marotti,, "Gogo lays off 55 as it seeks to turn around struggling in-flight Wi-Fi business," 13 July 2018 In 2017, security researchers sounded the alarm about Russian hackers infiltrating and probing United States power companies; there was even evidence that the actors had direct access to an American utility's control systems. Lily Hay Newman, WIRED, "The Worst Cybersecurity Breaches of 2018 So Far," 9 July 2018 No longer just the province of frat guys and truck drivers, the ball cap has been infiltrating menswear’s more upscale corridors. Scott Christian, WSJ, "Can Men Wear a Baseball Cap Without Looking Like a Frat Boy?," 19 June 2018 Surfer Girls in Spirit Menswear is experiencing a beachwear renaissance, and the idea has infiltrated the women’s Resort collections. Steff Yotka, Vogue, "The Resort 2019 Trend Report," 25 June 2018 The briefings came after House Intelligence Chairman Devin Nunes demanded more information about the source -- a push that has prompted Trump to publicly speculate whether the FBI infiltrated his campaign. Ashley Killough And Manu Raju, CNN, "Ryan says he agrees with Gowdy that FBI acted appropriately," 6 June 2018 Case in point: Trump’s lie that the FBI infiltrated his campaign with spies. Trudy Rubin,, "Putin's info war against America amplified by Trump | Trudy Rubin," 30 May 2018 Spygate,’ an as-yet unproven allegation that the FBI infiltrated the Trump campaign for political purposes. Natasha Bach, Fortune, "'It Is for Public Opinion.' Rudy Giuliani May Have Admitted That Trump's 'Spygate' Is a PR Ploy," 28 May 2018 The film looks like a twist on a ’70s cop movie that turns it into a comedy about a black cop trying to infiltrate the KKK. Jacob Kastrenakes, The Verge, "New trailers: Bohemian Rhapsody, Mission: Impossible - Fallout, and more," 19 May 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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Statistics for infiltrate

Last Updated

15 Oct 2018

Look-up Popularity

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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Comments on infiltrate

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lying above or upon

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