v. i. [ imp. & p. p. Infiltrated p. pr. & vb. n. Infiltrating ] [ Pref. in- + filtrate: cf. F, s'infiltrer. Cf. Infilter. ] 1. To enter by penetrating the pores or interstices of a substance; to filter into or through something. [ 1913 Webster ]
The water infiltrates through the porous rock. Addison. [ 1913 Webster ]
2. To enter secretly (into an organization, territory, etc.) for hostile purposes, such as spying or sabotage; as, the FBI infiltrated into the U. S. communist party's upper echelons; also used transitively; as, to infiltrate the opponent's organization; to infiltrate one's agents into a hostile country. [ PJC ]