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

• 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

Words change meaning over time, slang infiltrates the mainstream, and sometimes, a little creative license is acceptable. —Jerry Weissman, Forbes.com, 26 June 2025

Such attacks have already infiltrated U.S. water and wastewater systems, according to the non-profit think tank Center for Internet Security, which briefed law enforcement on Friday. —Pierre Thomas, ABC News, 21 June 2025

There is this massive explosion that happens when you guys infiltrate Grady's farmhouse. —EW.com, 20 June 2025

On Law & Order: Organized Crime, Stabler joined the New York Police Department's Organized Crime Control Bureau to infiltrate the world of seedy crime syndicates, including some that wish to seek revenge on him and his family. —Christopher Rudolph, People.com, 13 June 2025

Word History

First Known Use

1758, in the meaning defined at transitive sense 4

Rhymes for infiltrate

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

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