IPA: /ˈiːvəl.nəs/
KK: /ˈivəlˌnəs/
The quality or state of being morally bad or wicked.
The villain's evilness was evident in his cruel actions.
Evilness is formed from "evil" (from Old English *yfel*, meaning morally bad or wicked) and "-ness" (a suffix meaning the state or quality of). The word "evilness" refers to the state or quality of being evil or morally bad.
Think of the word 'evil' to remember that 'evilness' means the state of being evil.