infiltration has 1 distinct synonym spread across 1 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a process in which individuals (or small groups) penetrate an area (especially the military penetration of enemy positions without detection)
the slow passage of a liquid through a filtering medium
“the percolation of rainwater through the soil”
Synonyms, antonyms and the broader and narrower relations for infiltration come from Princeton University’s WordNet. Full sources and licences.