What does infiltrate mean?
Infiltrate means to enter, join, or gain access to something in a covert or gradual manner. Its best-known sense is entering an organization, institution, security system, or territory secretly, often for an improper purpose, as when investigators infiltrate a criminal group or unauthorized users infiltrate a computer network. The verb can also describe influence spreading subtly through a political party or other body. A more technical use refers to liquid passing gradually into porous material, such as water infiltrating soil. The word is common in political, military, journalistic, and cybersecurity language and often carries a negative implication because the entry is typically unauthorized, deceptive, or clandestine. Although “infiltrate” can simply mean “penetrate,” it usually suggests concealment or a gradual process rather than ordinary, visible entry.
To enter, join, or gain access to a place, group, organization, or system secretly or gradually, especially for an improper or covert purpose; to spread subtly through something.
"The group tried to infiltrate the police organization by obtaining false identities."
The verb may be transitive or intransitive. Its common figurative uses imply secrecy, concealment, or gradual penetration, while its use for liquids is more technical.
A person who secretly joins an organization, group, or place, especially as an agent or infiltrator.
"The undercover officers were accepted as infiltrates by the organization."
The noun is rare in modern usage; “infiltrator” is generally preferred for a person who enters a group covertly.
The plural is formed by adding -s, although the noun itself is uncommon and “infiltrators” is normally used instead.
"The investigators suspected that several infiltrates remained within the group."
The word began with the image of passing a liquid through a filter; its best-known military sense later turned filtering into a metaphor for slipping unseen into enemy ranks.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does infiltrate come from?
Infiltrate entered English in the early 17th century from Modern Latin infiltratus, the past participle of infiltrare, formed from the prefix in- and Latin filtrare, “to filter.” The filtering verb is related to Latin filum, meaning “thread,” an expression of the material used to strain liquids. By the early 19th century, the word had developed the now-familiar figurative sense of entering secretly, especially into military ranks or an organization.
Related word forms
How infiltrate is actually used
The verb is used in political, military, security, criminal, and computing contexts, where it often implies deception or lack of authorization. In general contexts, it can also mean entering or becoming established gradually. The noun use is rare; “infiltrator” is usually more natural when referring to a person who infiltrates.