diabolic

UK: /ˌdaɪəˈbɒlɪk/ US: /ˌdaɪəˈbɑlɪk/ ,(dī′ə bol′ik)

WordReference Random House Learner's Dictionary of American English © 2025

di•a•bol•ic /ˌdaɪəˈbɑlɪk/  also ˌdi•aˈbol•i•cal, adj. 

1. devilish;
   fiendish;
   extremely wicked:
   a diabolic plot to kill the president.
2. relating to or caused by a devil.

di•a•bol•i•cal•ly, adv. 
di•a•bol•i•cal•ness, n. [uncountable]

WordReference Random House Unabridged Dictionary of American English © 2025

di•a•bol•ic  (dī′ə bol′ik), adj. 

1. having the qualities of a devil;
   devilish;
   fiendish;
   outrageously wicked:
   a diabolic plot.
2. pertaining to or actuated by a devil.

Also, di′a•bol′i•cal. 

• Greek diabolikós, equivalent. to diábol(os) devil + -ikos -ic
• Late Latin diabolicus
• Middle French)
• Middle English diabolik (1350–1400

di′a•bol′i•cal•ly, adv. 
di′a•bol′i•cal•ness, n. 

Collins Concise English Dictionary © HarperCollins Publishers::

diabolic / ˌdaɪəˈbɒlɪk/ adjective

1. of, relating to, or proceeding from the devil; satanic
2. befitting a devil; extremely cruel or wicked; fiendish
3. very difficult or unpleasant

Etymology: 14th Century: from Late Latin diabolicus, from Greek diabolikos, from diabolos devil