Infernal is an adjective that is commonly used to describe something that is extremely unpleasant, irritating or hellish. When it comes to synonyms for this word, you have a few options to choose from. Words like diabolical, satanic, demonic, fiendish, hellish, and demonic are all great alternatives. Each of these synonyms carries its own unique connotations and can be used to convey the same or similar meanings as infernal. Other synonyms for infernal include tormenting, malevolent, evil, and sinister. These words are all great for describing something that is unpleasant or difficult to deal with. In summary, there are many synonyms for the word infernal, each with its own nuances and flavors.