from
The Collaborative International Dictionary of English v.0.48
Infiltrate \In*fil"trate\, 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]