infiltrate

Etymology

From Middle English infiltrate (adj), from Medieval Latin infiltrātus, from infiltrō.

verb

1. (transitive, intransitive) To surreptitiously penetrate, enter or gain access to.
   The spy infiltrated the high-tech company and stole many secrets.
2. (transitive) To cause to penetrate in this way.
   The agency infiltrated several spies into the company.
3. (transitive, intransitive, of a liquid) To pass through something by filtration.
4. (transitive) To cause (a liquid) to pass through something by filtration.
5. (transitive, intransitive, medicine) To invade or penetrate a tissue or organ.
   High-grade tumors often infiltrate surrounding structures.
   In certain conditions, immune cells may infiltrate into the cerebrospinal fluid.
6. (transitive, military) To send (soldiers, spies, etc.) through gaps in the enemy line.
7. (intransitive, of an intravenous needle) To move from a vein, remaining in the body.

noun

1. (pathology) Any undesirable substance or group of cells that has made its way into part of the body.
   One critical distinction to make is whether a focal corneal infiltrate is infected with bacteria or is a sterile immunologic response. 2008, Jimmy D. Bartlett, Siret D. Jaanus, Clinical Ocular Pharmacology, page 539