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 infiltration (audio) \ noun
infiltrative \ ˈin-​(ˌ)fil-​ˌtrā-​tiv How to pronounce infiltrative (audio) , in-​ˈfil-​trə-​ \ adjective
infiltrator \ ˈin-​(ˌ)fil-​ˌtrā-​tər How to pronounce infiltrator (audio) , in-​ˈfil-​ How to pronounce infiltrator (audio) \ noun

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 Narcosubs are designed to infiltrate coastlines, not invade them, slowly making their way across the Eastern Pacific and Carribean from South America to Central America and even as far as Europe. Kyle Mizokami, Popular Mechanics, "DEA Busts Electric-Powered Narcosub That Can Carry 6 Metric Tons of Cocaine," 18 Nov. 2020 The group continues to expand its bomb-making operations, infiltrate government institutions and carry out attacks against civilian and security targets in both Kenya and Somalia. Eric Schmitt, New York Times, "Somalia Worries That a U.S. Withdrawal Will Be Disastrous," 18 Nov. 2020 Astral Chain is a Switch exclusive that tasks players with joining the Neuron special police task force, working to infiltrate the Astral Plane. Brittany Vincent, CNN Underscored, "These are our favorite games for the Nintendo Switch and Switch Lite," 13 Nov. 2020 When inhaled at high enough levels, the bacteria can infiltrate the lungs and cause one of two forms of legionellosis, Pontiac fever or Legionnaires’ disease. Lynne Peeples Ensia, Smithsonian Magazine, "Why Reports of Legionnaires’ Disease Are on the Rise in the United States," 22 Oct. 2020 Healthy soil also allows much more water to infiltrate and be filtered versus running off and causing erosion and carrying pollution into watersheds. Outdoor Life, "In the Future: Hunters Will Geek Out on Soil Science," 14 Oct. 2020 Instead, the researchers say, Nebraska’s sandier soils allow more rain to infiltrate into the ground and recharge the aquifer. Scott K. Johnson, Ars Technica, "Projecting “peak water” and “peak grain” for the US High Plains," 6 Oct. 2020 But even so, when May tries to talk to Kora about Malick and her mother, Kora ends up overreacting and using her powers to short-circuit the Lighthouse’s power, allowing Sybil to infiltrate their system. Christian Holub,, "Agents of S.H.I.E.L.D. recap: The end is near," 6 Aug. 2020 This massive production of T cells that infiltrate your lungs, throat, and nose cause inflammation, swelling, and pain. Claire Maldarelli, Popular Science, "An exhaustive account of how the flu destroys your body," 22 Feb. 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 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

25 Nov 2020

Cite this Entry

“Infiltrate.” Dictionary, Merriam-Webster, Accessed 30 Nov. 2020.

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More Definitions for infiltrate


How to pronounce infiltrate (audio) How to pronounce infiltrate (audio)

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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