The quality or state of being dissatisfactory; the degree to which something fails to satisfy or meet expectations.
From 'dissatisfactory' plus the noun-forming suffix '-ness.' This creates a double negation at the prefix level, making it an abstract noun describing the property of being unsatisfactory.
Words this long and complex (13 syllables!) often appear in academic writing or complaints—there's something appropriately heavyweight about needing such a ponderous word to describe how disappointed you are!
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