Eftiuvium is not a commonly used word. However, there are several synonyms for this word that can be used in its place. Some of these synonyms include effluvium, emanation, exhalation, fume, gas, odor, smog, smoke, and vapor. Effluvium is a particularly useful synonym as it specifically refers to gases or vapors that are emitted from a substance. This word can be used in contexts where eftiuvium might seem out of place, or where a more widely recognized word is necessary for clarity. Overall, these synonyms provide alternative ways to talk about gaseous substances or odors.