infiltrate
UK: ˈɪnfɪltreɪt | US: ˈɪnfɪltreɪt
vt. to enter or gain access to (an organization, place, etc.) secretly and gradually, especially for hostile purposes
vi. to pass through a substance or area by filtering or permeating
The word "infiltrate" originates from the Latin infiltrare, combining in- (into) and filtrum (filter). The concept reflects liquid passing through a filter, later metaphorically extended to describe covert entry into groups or systems. The modern sense of stealthy penetration (e.g., spies or fluids) emerged in the 18th century, blending physical and abstract meanings.
The spy managed to infiltrate the enemy’s headquarters undetected.
Water can infiltrate porous rocks over time.
The virus infiltrates the body’s immune system.
Activists infiltrated the meeting to expose corruption.
Dyes were used to show how chemicals infiltrate the soil.