c. 1500, "pertaining to the devil," from diabolic + -al (1). Meaning "befitting the devil" is from 1540s. Related: Diabolically.
the diabolical expression on his face
diabolical sorcerers under the influence of devils
di-
dia-
diabetes
diabetic
diabolic
diabolical
diabolism
diachronic
diacritic
diadem
diagnose
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