intransitive verb, transitive verb infiltrated -·trat′ed, infiltrating -·trat′·ing

1. to pass, or cause (a fluid, cell, etc.) to pass, through small gaps or openings; filter
2. to pass through, as in filtering
3. to pass, or cause (individual troops) to pass, through weak places in the enemy's lines in order to attack the enemy's flanks or rear
4. to penetrate, or cause to penetrate (a region or group) gradually or stealthily, so as to attack or to seize control from within

Etymology: in- + filtrate

noun