infiltrate

verb

in·​fil·​trate ˈin-(ˌ)fil-ˌtrāt  in-ˈfil- 

infiltrated; infiltrating

transitive verb

1

: to enter or become established in gradually or unobtrusively usually for subversive purposes

the intelligence staff had been infiltrated by spies

2

: to pass (troops) singly or in small groups through gaps in the enemy line

3

: to pass into or through (a substance) by filtering or permeating

4

: to cause (something, such as a liquid) to permeate something by penetrating its pores or interstices

intransitive verb

: to enter, permeate, or pass through a substance or area by filtering or by insinuating gradually

infiltrate noun

infiltration

ˌin-(ˌ)fil-ˈtrā-shən 

noun

infiltrative

ˈin-(ˌ)fil-ˌtrā-tiv 

in-ˈfil-trə-

adjective

infiltrator

ˈin-(ˌ)fil-ˌtrā-tər  in-ˈfil- 

noun

Synonyms

• insinuate
• slip
• sneak
• wind
• work in
• worm
• wriggle

Examples of infiltrate in a Sentence

The gang was infiltrated by undercover agents.

Attempts to infiltrate undercover agents into the gang have failed.

Water can easily infiltrate the soil.

Recent Examples on the Web

So begins an elaborate plot to infiltrate a graphic designer awards event to confront his tormentor head-on. —Eric Berger, Ars Technica, 14 Feb. 2025

The flooding led to water infiltrating 16 first-floor units and the management office at Betty Ann Gardens Apartments. —Nollyanne Delacruz, The Mercury News, 13 Feb. 2025

One such technique involves malicious GIF images that exploit worm-like vulnerabilities, allowing attackers to take over accounts and infiltrate chat sessions when the image is opened. —Kurt Knutsson, Cyberguy Report, Fox News, 10 Feb. 2025

The socks have apparently infiltrated a Pre-K class in Bed-Stuy. —Adriane Quinlan, Curbed, 7 Feb. 2025

Word History

First Known Use

1758, in the meaning defined at transitive sense 4

Kids Definition

infiltrate

verb

in·​fil·​trate in-ˈfil-ˌtrāt  ˈin-(ˌ)fil- 

infiltrated; infiltrating

1

: to pass into or through by filtering

2

: to enter or become established gradually or secretly

infiltration

ˌin-(ˌ)fil-ˈtrā-shən 

noun

infiltrator

in-ˈfil-ˌtrāt-ər  ˈin-(ˌ)fil- 

noun

Medical Definition

infiltrate

1 of 2 verb

in·​fil·​trate in-ˈfil-ˌtrāt  ˈin-(ˌ) 

infiltrated; infiltrating

transitive verb

1

: to cause (as a liquid) to permeate something by penetrating its pores or interstices

infiltrate tissue with a local anesthetic

2

: to pass into or through (a substance) by filtering or permeating

intransitive verb

: to enter, permeate, or pass through a substance or area

infiltrate

2 of 2 noun

: something that passes or is caused to pass into or through something by permeating or filtering

especially : a substance that passes into the bodily tissues and forms an abnormal accumulation

a lung infiltrate