happiness

Happiness is built from happy plus the suffix -ness. Happy traces back through Middle English hap to Old Norse happ, meaning luck or chance, ultimately from a Proto-Indo-European root meaning to fit or suit.

Hap once simply meant luck or fortune — good or bad. Happy grew from it to mean lucky, then fortunate, before settling into the feeling of contentment we know today, and -ness turned that quality into a noun.

It shares its root with happy itself, the word from which happiness was directly formed by adding -ness.