To surreptitiously penetrate, enter or gain access to.
(of a liquid) To pass through something by filtration.
To cause (a liquid) to pass through something by filtration.
To invade or penetrate a tissue or organ.
High-grade tumors often infiltrate surrounding structures.
To send (soldiers, spies etc.) through gaps in the enemy line.
(of an intravenous needle) To move from a vein, remaining in the body.