DIABOLICAL(adj): Something that is extremely evil or cruel
Synonyms– poor, dreadful, awful, terrible, frightful, disgraceful
Antonyms– Angelic, Benevolent, Good, Kind, Virtuous, Moral, Righteous, Saintly, Honorable, Pure
Sentence usage– The prank he played on his friend was diabolical and made everyone upset.
Phrase/Idiom– Heart of stone, a person who is unfeeling, cruel, or merciless.