tristeza
/tɾisˈteθa/ · B1 · noun · f
sadness
🌧️ triste (sad) + -eza (-ness) = sadness, from Latin tristitia
The suffix -eza turns adjectives into nouns, like belleza from bello and pobreza from pobre. Triste comes from Latin tristis, the same root as the rare English word tristful. Tristeza is feminine, so you say la tristeza.