infiltrate - Dictionary definition and meaning for word infiltrate
IN+FILTER(water filter)....In filters water INFILTRATES through porous membrane so that the impurities are removed....
When an object is able to filter something, some part will stay in it and other part will 'PASS THROUGH' it. Imagine you are filtering your morning 'TEA'.
infiltrate:in(not)+filtrate(filter)-so if you are not filtering anything then it means you allow it to pass through.