The Spanish word 'diurno' (meaning 'diurnal' or 'relating to daytime') comes from the Latin word 'diurnus', which meant 'of or belonging to the day'. The Latin word 'diurnus' was formed by combining two elements: 'dies' meaning 'day' and the suffix '-urnus' meaning 'belonging to'. This combination literally created a word meaning 'belonging to the day'.

Some related Spanish words include 'día' (day), which comes from the same Latin root 'dies'. Another related word is 'diario' (daily), which shows how this word family in Spanish consistently relates to concepts of day and daily activities.

English speakers might recognize this word's connection to 'diurnal' (active during the day), which comes from the same Latin source. The word 'diary' is also related, coming from Latin 'dies' (day), as it originally referred to a daily record. Even the word 'journal' is distantly related, as it comes from Latin 'diurnalis' meaning 'daily'.