"Fiend angelical" is an oxymoron, a phrase that combines two contrasting words to create a paradoxical effect. The word "fiend" implies evil and malevolence, whereas "angelical" suggests purity and goodness. Synonyms could include "dark cherub," "demonic seraph," or "sinful celestial." These contradictory terms seek to describe someone or something that is both good and bad, challenging and complex. As language evolves, new oxymoronic phrases may arise to capture similarly paradoxical qualities. Regardless of the phrasing, these terms capture the complicated nuance of those who defy simple categorization, and typify the rich diversity of human nature.