infiltrate
v.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.
v.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.
“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.”
The verb is transitive and takes a direct object.
“Undercover agents infiltrated meetings, private chats and local events.”
“In both areas, Russia has captured territory and infiltrated large areas beyond it, but this has come at a cost.”
From Middle English infiltrate (adjective), from Medieval Latin infiltrātus, from infiltrō.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.