infiltration

American  

[in-fil-trey-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

Etymology

Origin of infiltration

First recorded in 1790–1800; infiltrate + -ion

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

Analysts estimate the area is smaller and that Ukraine has mainly cleared the area of Russian infiltration teams.

From The Wall Street Journal • Feb. 24, 2026

One tactic was by far the most effective: infiltration.

From Salon • Feb. 15, 2026

California banned phones in public school classrooms beginning in January, largely in response to the infiltration of social media.

From Los Angeles Times • Feb. 9, 2026

One man has claimed responsibility for the infiltration, saying he did so to detect radiation levels from the North's Pyongsan uranium processing facility.

From Barron's • Jan. 21, 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

Related Words

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