infiltration

American  

[in-fil-tray-shuhn] / ˌɪn fɪlˈtreɪ ʃən /

noun

1. the act or process of infiltrating.

2. the state of being infiltrated.

3. something that infiltrates; an infiltrate.

4. Military.

   1. a method of attack in which small bodies of soldiers or individual soldiers penetrate the enemy's line at weak or unguarded points in order to assemble behind the enemy position and attack it from the rear, harass enemy rear-area installations, etc.

   2. a system of transporting troops or vehicles at extended and irregular intervals so as to avoid enemy observation or attack, especially from the air.

5. Geology. the seepage of water into soil or rock.

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Other Word Forms

• reinfiltration
  noun

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Etymology

Origin of infiltration

First recorded in 1790–1800; infiltrate + -ion

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Explanation

When infiltration happens in an ecosystem, it means water soaks down into the soil. When infiltration happens in a spy movie, it means that someone sneaks into a place to learn secret information. Military or security infiltration happens when troops penetrate their enemy's front lines to attack more vulnerable areas, or when CIA agents go undercover, posing as members of a group in order to gather information. In science, infiltration generally refers to rainwater being absorbed by the ground, or groundwater entering sewers and causing overflows that harm the environment.

Example Sentences

See Examples For:

infiltration

Despite lifting the state of emergency, the authorities remain wary of RSF infiltration.

From BBC ● Aug. 28, 2026

Troops sent on infiltration missions are often ex-convicts given only days of training, since walking to an assigned location and awaiting further orders requires minimal proficiency, Kofman said.

From The Wall Street Journal ● May 12, 2026

"We show that increased infiltration of T cells that are attacking tumor cells translates into a therapeutic benefit for patients with glioblastoma," said Chiocca, who is also a co-senior author of the study.

From Science Daily ● Mar. 20, 2026

The group said its fighters had "observed the infiltration of four Israeli enemy army helicopters from the Syrian direction".

From Barron's ● Mar. 7, 2026

Two years after the recording of ‘Strange Fruit’, Meeropol was summoned to appear before New York State’s Rapp-Coudert committee investigating alleged Communist infiltration of the state’s high schools.

From "The Story of Music" by Howard Goodall

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Related Words

• aggression
• assault
• breach
• incursion
• infringement
• intrusion
• offensive
• onslaught
• raid
• violation

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