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 of infiltrate

• sneak
• worm
• insert
• slip
• work in

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

Gotta hand it to Odysseus — having a bunch of soldiers hide inside a giant horse to infiltrate Troy worked out beautifully. — Whitney Friedlander, Vulture, 17 July 2026

Local growers are less likely to have contaminated water sources for irrigation, which is one way the parasite can infiltrate produce. — Sara Moniuszko, USA Today, 16 July 2026

The eight-part Spanish-language drama, inspired by real events, is set in 1980s Lima, Peru, and follows the rise of an elite law school cabal that infiltrates academia, politics, and organized crime. — Andreas Wiseman, Deadline, 15 July 2026

If 2025 was the year AI infiltrated every corner of consumer life — from social feeds to shopping — 2026 is the year people are pausing for thought. — Amy O’Brien, Vogue, 14 July 2026

Word History

First Known Use

1758, in the meaning defined at transitive sense 4

Rhymes for infiltrate

• abdicate
• abrogate
• acetate
• activate
• actuate
• aggravate
• agitate
• alginate
• alienate
• allocate
• amputate
• angulate

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