IPA: //ʌn.fəˈɡɪv.ɪŋ.nəs//
KK: /ʌnˈfɔrɪɡɪŋnəs/
The quality of not forgiving or being harsh and strict towards others.
Her unforgivingness made it difficult for her to maintain friendships.
Unforgivingness → It is formed from "un-" (meaning not), "forgiving" (from Old English "forgiefan", meaning to give up resentment), and "-ness" (meaning the state of being). The word "unforgivingness" refers to the state of not giving up resentment or being unwilling to forgive.
Think of 'not' ('un-') being willing to 'give up resentment' ('forgiefan') — that's why unforgivingness means the state of holding onto resentment.