IPA: /ˈɪnfɪltreɪtɪv/
KK: /ɪnˈfɪltrətɪv/
Describing something that is capable of entering or spreading into a place or system, often in a secretive or stealthy manner.
The infiltrative tactics used by the spy allowed him to gather information without being detected.
Infiltrative → It is formed from "in-" (meaning into) and "filtrare" (meaning to filter). The word describes the action of filtering or penetrating into a substance or area.
Think of something that is 'filtering in' ('in-') — that's why infiltrative means something that penetrates or filters into another.