The word "soiliest" refers to something that is the most dirty or contaminated with soil. In antonyms or opposite words, we can refer to something that is the cleanest or free from soil. The antonyms for "soiliest" include "cleanest," "purest," "sterile," "unsullied," "immaculate," "spotless," "unblemished," "unsoiled," "uncontaminated" and "unpolluted." These words indicate something that is opposite from "soiliest," which gives a sense of cleanliness, hygiene and purity. It is interesting to note that antonyms, along with synonyms, enable us to communicate more clearly, especially when we need to express a different idea or perspective.