GRE diabolical Definition Extremely evil or cruel; devilish. Example "The villain's diabolical plan threatened to destroy the city." Sign in to save GRE Quiz → ← diabetes diagnose → Study tips featuring "diabolical" Write GRE Words Into Your Own Sentences Related words GRE swill GRE taper GRE testy GRE abacus SAT abase GRE abash GRE abate GRE abbreviate GRE abbreviation SAT abdicate SAT abdomen GRE abduct