IPA: /nɒnˈfiːzəns/
KK: /nɑnˈfiːzəns/
Not doing something that you are supposed to do, especially in a legal or official context.
The city was sued for nonfeasance after it failed to repair the dangerous road.
Nonfeasance is formed from "non-" (meaning not) and "feasance" (from Latin "facere", meaning to do or make). The term refers to the failure to act or perform a duty that one is obligated to do.
Think of 'not doing' ('non-') something that you are supposed to 'do' ('facere') — that's what nonfeasance means.