Other forms: infiltrated, infiltrating, infiltrates
To infiltrate is to get inside a group in order to watch it. Infiltrate the organisation, infiltrated by agents, infiltrate a network.
It means entering by concealment rather than by force, which is what separates it from invade. Police, intelligence services and journalists all do it, and the legal limits on how far an undercover officer may go are one of the harder questions in policing. The literal sense is of liquid seeping through: water infiltrates the soil, which is a technical term in hydrology. Note infiltrator, infiltration.
1verbinfiltrateTo get inside a group in order to watch it.
“An undercover journalist infiltrated the gang and secretly recorded their meetings.”
2verbseepTo seep gradually through something.
“Rainwater slowly infiltrated the soil and filled the caves below.”
infiltrate is an entering by stealth.
Medieval Latin infiltrare is in plus filtrum, felt — the material early filters were made of. To infiltrate is to seep through felt, and filter is the same word.
Medieval Latin
infiltrātus
Middle English
infiltrate
English, today
infiltrate
From Middle English infiltrate, from Medieval Latin infiltrātus, from infiltrō.
Etymology from Wiktionary, CC BY-SA
Practised in Spying & Secrecy