Diabolical means wickedly clever or evil, like something a villain in a story would devise. When someone creates a diabolical plan, they've thought of something so cunning and malicious that it seems almost supernaturally clever.

In stories, diabolical villains don't just want to win: they want to win in the most elaborate, twisted way possible. A diabolical trap might have layers of deception, secret mechanisms, and backup plans. Think of the evil queen in Snow White transforming herself into an old woman and offering a poisoned apple: that level of calculated wickedness is diabolical.

People sometimes use the word playfully for things that are fiendishly difficult or frustrating. A teacher might create a diabolical puzzle for a challenge activity, one so tricky it makes students scratch their heads. A diabolically complicated maze or an escape room with sneaky tricks could earn the label too. In these cases, diabolical means ingeniously difficult rather than truly evil, though there's still that hint of mischievous pleasure in creating something so challenging.