Unhappiness is a settled state of not being happy. Deep unhappiness, the unhappiness of the arrangement, express unhappiness.
It is milder and broader than depression and it names a situation as often as a mood — unhappiness at work is a complaint about conditions. Note the three parts: un-, happy and -ness, and that happy first meant lucky.
1noununhappinessA settled state of not being happy.
“Years of unhappiness in her marriage finally led her to leave.”
unhappiness is a state of mind.
Un- plus happy plus -ness. Happy comes from hap, chance, so the word first concerned luck rather than mood.
From unhappy + -ness or un- + happiness.
Etymology from Wiktionary, CC BY-SA