The Spanish word 'tristeza' meaning 'sadness' comes from the Latin word 'tristitia', which also meant 'sadness'. 'Tristitia' itself was derived from the Latin adjective 'tristis' meaning 'sad'. The evolution from Latin to Spanish shows a common sound change where the '-itia' ending in Latin became '-eza' in Spanish, which is a pattern seen in other Spanish words as well.

A simpler and very common related Spanish word is 'triste', which means 'sad'. This adjective comes directly from the Latin 'tristis' and is used frequently in everyday Spanish. You might hear phrases like 'estoy triste' (I am sad) before you encounter the noun form 'tristeza'.

While English doesn't have many common words directly related to 'tristeza', you might encounter 'tristful' (meaning sad or melancholy) in literary contexts, though it's quite rare. The word 'trist' also exists in English as an archaic term for 'sad' or 'gloomy', but it's virtually never used in modern English. However, you might recognize the mood or feeling that 'tristeza' conveys in English words like 'distress', though this comes from a different Latin root.