infiltrate

American  

[in-fil-treyt, in-fil-treyt] / ɪnˈfɪl treɪt, ˈɪn fɪlˌtreɪt /

verb (used with object)

infiltrated, infiltrating

1. to filter into or through; permeate.

2. to cause to pass in by filtering.

3. to move into (an organization, country, territory, or the like) surreptitiously and gradually, especially with hostile intent.

   The troops infiltrated the enemy lines.

4. to pass a small number of (soldiers, spies, or the like) into a territory or organization clandestinely and with hostile or subversive intent.

   The intelligence agency infiltrated three spies into the neighboring country.

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verb (used without object)

infiltrated, infiltrating

1. to pass into or through a substance, place, etc., by or as by filtering.

2. Pathology. to penetrate tissue spaces or cells.

noun

1. something that infiltrates.

2. Pathology. any substance penetrating tissues or cells and forming a morbid accumulation.

infiltrate British  

/ ˈɪnfɪlˌtreɪt /

verb

1. to undergo or cause to undergo the process in which a fluid passes into the pores or interstices of a solid; permeate

2. military to pass undetected through (an enemy-held line or position)

3. to gain or cause to gain entrance or access surreptitiously

   they infiltrated the party structure

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noun

1. something that infiltrates

2. pathol any substance that passes into and accumulates within cells, tissues, or organs

3. pathol a local anaesthetic solution injected into the tissues to cause local anaesthesia

Other Word Forms

• infiltration noun
• infiltrative adjective
• infiltrator noun
• reinfiltrate verb
• uninfiltrated adjective

Etymology

Origin of infiltrate

First recorded in 1750–60; in- ² + filtrate

Example Sentences

For Epstein, money was the primary means to infiltrate cash-hungry academic institutions, which can employ hundreds of people in their development offices.

From The Wall Street Journal • Feb. 26, 2026

Dan and Tamma are climbing toward something, of course: He’s pursuing a college scholarship and she is determined to infiltrate the world of professional climbers.

From Los Angeles Times • Jan. 20, 2026

Besides having foiled some 600 assassination attempts against late leader Fidel Castro, Cuba was reputed for its ability to infiltrate foreign intelligence services and recruit high-ranking informants, particularly Americans.

From Barron's • Jan. 10, 2026

There are fears that, now the rainy season has started, heavy metals still sitting in the mud will further infiltrate the land and waterways, causing a second wave of pollution.

From BBC • Dec. 2, 2025

That summer, the team of operatives hired by Mathis began to infiltrate Osage County.

From "Killers of the Flower Moon" by David Grann

Related Words

• penetrate
• permeate
• pervade