12 letters · 15 points in Scrabble
noun a process in which individuals (or small groups) penetrate an area (especially the military penetration of enemy positions without detection)
noun the slow passage of a liquid through a filtering medium
originFrom Middle English infiltracioun, from Medieval Latin infiltrātiōnem, infiltrātiō. By surface analysis, infiltrat(e) + -ion.
Etymology from Wiktionary, CC BY-SA 3.0