verb
(ambitransitive) To surreptitiously penetrate, enter or gain access to.
(transitive) To cause to penetrate in this way.
(ambitransitive, of a liquid) To pass through something by filtration.
(transitive) To cause (a liquid) to pass through something by filtration.
(ambitransitive, medicine) To invade or penetrate a tissue or organ.
(transitive, military) To send (soldiers, spies, etc.) through gaps in the enemy line.
(intransitive, of an intravenous needle) To move from a vein, remaining in the body.
noun
(pathology) Any undesirable substance or group of cells that has made its way into part of the body.