Demon is a word commonly used to refer to evil spirits or supernatural entities. However, there are many other words that can be used as synonyms to describe such entities. One of the most common alternative words is devil, which is also used to describe evil spirits. Other synonyms for demon include fiend, hellion, imp, incubus, succubus, monster, and phantom. Some of these synonyms might be region-specific or culture-specific, and their meanings could have different nuances. Regardless, they all represent malevolent entities that are often associated with evil, mischief and darkness.