infiltration

noun

1. (countable, uncountable)The act or process of infiltrating, as of water into a porous substance, or of a fluid into the cells of an organ or part of the body.
2. (countable, uncountable)The act or process of infiltrating, as of water into a porous substance, or of a fluid into the cells of an organ or part of the body.
3. (countable, uncountable)The substance which has entered the pores or cavities of a body.

   “calcareous infiltrations filling the cavities”

4. (countable, uncountable)The act of secretly entering a physical location and/or organization.

   “No one should be under any illusions about the objective of the Communist Party leadership: it’s long-term, systematic infiltration of social organisations, media and government. By the time China’s infiltration of Australia is readily apparent, it will be too late.”