Source : Webster's Revised Unabridged Dictionary (1913)

Infiltrate \In*fil"trate\, v. i. [imp. & p. p. {Infiltrated}; p.
   pr. & vb. n. {Infiltrating}.] [Pref. in- + filtrate: cf. F,
   s'infiltrer. Cf. {Infilter}.]
   To enter by penetrating the pores or interstices of a
   substance; to filter into or through something.

         The water infiltrates through the porous rock.
                                                  --Addison.

Infiltrate \In*fil"trate\, v. t.
   To penetrate gradually; -- sometimes used reflexively. --J.
   S. Mill.

Source : WordNet®

infiltrate
     v 1: cause (a liquid) to enter by penetrating the interstices
     2: enter a group or organization in order to spy on the
        members; "The student organization was infiltrated by a
        traitor" [syn: {penetrate}]
     3: pass into or through by filtering or permeating; "the
        substance infiltrated the material"
     4: pass through an enemy-line; in a military conflict [syn: {pass
        through}]