1. extremely wicked or cruel; evil
2. extremely difficult or unpleasant
Usage: informal
3. relating to or characteristic of the devil

Examples

• The villain’s diabolical plan threatened the entire city.
• She gave him a diabolical smile before revealing her scheme.
• The traffic was absolutely diabolical this morning.
• The puzzle was so diabolical that no one could solve it.
• His diabolical laughter echoed through the haunted house.
• The weather has been diabolical all week.
• The ancient text described diabolical creatures from the underworld.