IPA: /ʌnˈfɪt.nəs/
KK: /ʌnˈfɪtnəs/
The state or quality of not being suitable or fit for a particular purpose or activity.
His unfitness for the job was evident during the interview.
Unfitness → It is formed from "un-" (meaning not) and "fitness" (from Old English "fittnes", meaning suitability or appropriateness). The word "unfitness" means the state of not being suitable or appropriate.
Think of 'not' ('un-') being added to 'suitability' ('fitness') — that’s why unfitness means not being suitable.