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

It is a paranoid reflex that turns any hint of infiltration into proof of betrayal.

From Salon • Apr. 25, 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

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

In July of that year, the committee announced a new round of investigations, but this time into something far more serious than the communist infiltration of Hollywood.

From "Spies: The Secret Showdown Between America and Russia" by Marc Favreau

Related Words

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