infiltration
Americannoun
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the act or process of infiltrating.
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the state of being infiltrated.
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something that infiltrates; an infiltrate.
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Military.
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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.
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a system of transporting troops or vehicles at extended and irregular intervals so as to avoid enemy observation or attack, especially from the air.
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Geology. the seepage of water into soil or rock.
Other Word Forms
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.
Vocabulary lists containing infiltration
The Water Cycle - Introductory
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Earth Science - Middle School
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The Water Cycle - Middle School and High School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
James Scobie KC, representing Lavrynovych, said he was a "complete and utter foot soldier" and "fodder for this type of infiltration".
From BBC ● Jun. 19, 2026
Unable to launch major offensive operations on the front, Russia has taken to launching infiltration operations: sending small groups of soldiers behind enemy lines to hold key positions until reinforcements arrive.
From Barron's ● Jun. 14, 2026
Russia shifted tactics in early 2025 toward infiltration, whereby small groups of soldiers are sent through gaps in Ukraine’s defensive lines.
From The Wall Street Journal ● May 12, 2026
It is a paranoid reflex that turns any hint of infiltration into proof of betrayal.
From Salon ● Apr. 25, 2026
I need not remind you about the attempted infiltration of a certain preserve in the interior of Brazil last year.
From "Fablehaven" by Brandon Mull
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
