Infiltrate

1. verb

   enter a group or organization in order to spy on the members

   “The student organization was infiltrated by a traitor”

   Similar: penetrate

2. verb

   cause (a liquid) to enter by penetrating the interstices

3. verb

   pass through an enemy line; in a military conflict

   Similar: pass through

4. verb

   pass into or through by filtering or permeating

   “the substance infiltrated the material”