infiltrate in WordNet English dictionary

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