IPA: /ˌdaɪəˈbɒlɪkəl/
KK: /daɪəˈbɑlɪkəl/
Relating to or resembling a devil, often in a very evil or cruel way.
The villain in the story had a diabolical plan to take over the world.
Diabolical → It is formed from "diabolus" (from Latin, meaning slanderer or accuser) and the suffix "-ical" (meaning pertaining to). The word "diabolical" refers to something that is characteristic of or befitting a devil, often implying wickedness or evil.
Think of the word 'diabolus' which means slanderer or accuser, and remember that 'diabolical' describes something that is devilish or wicked.