IPA: /ˌʌnəˈveɪlɪŋnəs/
KK: /ʌnəˈveɪlɪŋnəs/
The state of being ineffective or not producing the desired result; a lack of success or usefulness.
Despite their efforts, the unavailingness of their attempts to solve the problem was evident.
Unavailingness → It is formed from "un-" (meaning not), "availing" (from the verb "avail", which comes from Old French *availer*, meaning to be of use or benefit), and "-ness" (meaning the state or quality of). The word describes the state of being not useful or ineffective.
Think of 'not' ('un-') being combined with 'useful' ('availing') to remember that 'unavailingness' means the quality of being not useful.