1
also diabolic
: extremely evil
a diabolical [=fiendish, devilish] enemy
Note: Diabolical often describes a plot, scheme, etc., that is very clever and that is intended for an evil purpose.
2
British, informal
: very unpleasant, bad, or annoying
The party was awful: the guests were boring and the food was diabolical. [=awful, terrible]
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“Diabolical.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/diabolical. Accessed 19 Jun. 2026.
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