# infiltrate

/ˈɪnfɪɫˌtɹeɪt/ (US) · /ˈɪnfɪltɹˌeɪt/ (UK) · CEFR C1 · Verb

Source: https://englishreference.com/word/infiltrate
Updated: 2026-05-07

## Definition

to secretly enter a place or group to get information or cause damage. In medicine, it describes a liquid or substance slowly moving into a tissue or cell.

For teachers: to gain access to an organisation or place surreptitiously, typically for espionage or subversion. In a physiological context, refers to the permeation of a substance or cells into a tissue or organ.

## Examples

- The spy managed to infiltrate the enemy headquarters.
- Undercover officers were able to infiltrate the criminal gang and gather enough evidence for an arrest.
- The report detailed how extremist elements attempted to infiltrate local government committees to influence policy from within, while simultaneously maintaining a facade of moderate civic engagement.

## Usage notes

- The verb is transitive and takes a direct object.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.