Fiendlike is a strong adjective that describes someone or something that is devilish, cruel, or wicked. There are several synonyms for fiendlike, such as demonic, infernal, diabolical, malicious, monstrous, and savage. Each of these synonyms carries an intense and ferocious connotation, emphasizing the evil and merciless nature of the subject. For instance, demonic is used to describe something or someone that is fiendishly evil and infernal has a connotation of hellish torment. Similarly, diabolical implies something devilish, malicious describes someone who is deliberately cruel, while monstrous and savage carry connotations of inhuman cruelty and savagery. Overall, fiendlike is a powerful adjective that is best used when describing extreme wickedness and malevolence.