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

In 2014, Swedish naval forces investigated multiple reports of foreign submarine activity, and Stockholm confirmed that a unidentified foreign submarine had in fact infiltrated—and left—its waters. Kyle Mizokami, Popular Mechanics, "Mystery Submarine Spotted in Swedish Waters," 29 Oct. 2018 Neither adage proves nor disproves the claims of a highly sophisticated supply-chain attack infiltrating the world’s most powerful organizations. Dan Goodin, Ars Technica, "Bloomberg report says backdoored Supermicro hardware infiltrated major US telecom," 9 Oct. 2018 For our purposes, folks, the important thing is that the Obama administration infiltrated the Trump campaign with a spy. Jay Willis, GQ, "Spygate: How Right-Wing Media Creates a Conspiracy Theory Out of Thin Air," 23 May 2018 If decay has infiltrated the pulp of your tooth, a root canal may be necessary, Dr. Robles says. Korin Miller, SELF, "Is It Actually Possible to Get Rid of Cavities Without Fillings?," 17 Oct. 2018 Yeah, totally, that I’d sort of infiltrated my husband’s ... Eric Johnson, Recode, "Google’s former PR boss Jessica Powell wrote a satirical novel about tech and published it all on Medium," 2 Oct. 2018 In the chaos that followed, the NKVD — Stalin’s intelligence agency and forerunner of the KGB — made a mistake that would doom all the Soviet agents who would infiltrate the Manhattan Project, the top-secret American effort to build an atomic bomb. Tim Folger, Discover Magazine, "Chance Encounters," 17 Aug. 2018 She has been accused of attempting to infiltrate political groups to advance Russian interests. Madeleine Ngo, Vox, "#FreeMariaButina: Russia’s Foreign Ministry just launched a Twitter campaign for the accused spy," 19 July 2018 John David Washington plays Ron Stallworth, a black police officer in 1970s Colorado Springs who infiltrated a local chapter of the Ku Klux Klan over the phone, using a fellow officer (Adam Driver) as his stand-in at in-person meetings. Richard Lawson, HWD, "In Spike Lee’s Invigorating BlacKkKlansman, the Real Joke Is on Us," 14 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

10 Dec 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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