"Demonial" is an archaic term that refers to matters relating to demons or demonic entities. Synonyms for this word could include "diabolical", indicating something devilish or wicked in nature. Similarly, "infernal" can also be used to describe things associated with evil spirits or hellish qualities. Moreover, "satanic" conveys a more explicit reference to Satan or the devil. Other alternative words could be "demonic", "fiendish", or even "hellish", all emphasizing the malevolent or supernatural aspects of the topic at hand. While these synonyms capture the essence of "demonial", it's important to note that some of these terms may carry stronger religious connotations or focus specifically on the devil, depending on the context in which they are used.