Happiness
Etymology
From "hap" (luck, chance), from Old Norse "happ", plus "-ness." The buried root is telling: to be "happy" was once to be lucky — the same "hap" in "happen," "perhaps," and "mishap" — a reminder that early speakers saw good fortune, not achievement, behind a happy life.
noun · /HAP-ee-nuss/
A state of well-being ranging from momentary pleasure to lasting contentment.
What it names
The whole spectrum from a good mood to a good life, which is exactly why the single word causes so much confusion.
Example
He confused happiness with excitement for years, and only in a quiet, ordinary week finally recognized the deeper kind.
Related idea
Happiness in the fleeting sense is a feeling; eudaimonia is the older idea of a life well-lived and flourishing, which can hold steady through stretches that feel nothing like pleasure.