IPA: //ˈnæs.tɪ.nəs//
KK: /ˈnæs.tɪ.nəs/
The quality of being unpleasant, dirty, or morally offensive.
The nastiness of the situation made everyone uncomfortable.
Nastiness → It is formed from "nasty" (from Middle English *nasti*, meaning unpleasant or offensive) and the suffix "-ness" (meaning the state or quality of). The word "nastiness" refers to the state of being unpleasant or offensive.
Think of the word 'nasty' to remember that 'nastiness' means the quality of being unpleasant.