Infiltrate, which means to gain access to a group or organization, has a number of antonyms, or words with opposite meanings. One antonym is "exclude," meaning to keep someone or something out. Another is "eject," which means to force something or someone out. Additionally, "separate" or "distinguish" can be antonyms of infiltrate, meaning to break apart or differentiate. Finally, "expel" is another antonym for infiltrate that specifically refers to kicking someone or something out of a group, organization or area. All these antonyms convey a sense of removal, separation or isolation, which contrast with the meaning of infiltrate.