The Spanish word 'diéresis' comes from Ancient Greek through Latin. It was built from three Greek elements: 'dia-' meaning 'through', the verb 'haireo' meaning 'to take or seize', and the suffix '-sis' which forms action nouns. These combined to form 'diairesis' meaning 'division' or 'separation' in Greek. This word was borrowed into Latin as 'diaeresis', keeping the same meaning, and eventually made its way into Spanish as 'diéresis'.

Today in Spanish, 'diéresis' refers specifically to the diacritic mark (¨) placed over certain letters, particularly 'ü'. This meaning evolved from the original sense of 'division' or 'separation' because the mark indicates that two vowels that would normally form a single sound (diphthong) should be pronounced separately or 'divided' into two distinct sounds.

While 'diéresis' itself is a technical term in Spanish, the prefix 'dia-' appears in many common Spanish words like 'diálogo' (dialogue), 'diagonal' (diagonal), and 'diario' (daily), all carrying the sense of 'through' or 'across'.

English speakers might recognize this word in its English form 'diaeresis' or 'dieresis', which refers to the same diacritical mark. The same Greek elements appear in English words like 'dialogue' (speaking through/across), 'diameter' (measure through), and 'diagnosis' (knowing through). The suffix '-sis' is also familiar from words like 'analysis', 'synthesis', and 'thesis'.