The Spanish word 'común' (meaning 'common') comes from the Latin word 'communis', which also meant 'common' or 'shared'. The Latin word itself was formed by combining two elements: 'com-' meaning 'together' or 'with', and 'munis' meaning 'duty' or 'service'. So etymologically, something that is 'común' literally referred to sharing duties or services together with others, before generalizing to mean anything that is shared or common.

Several common Spanish words share this same Latin root, including: 'comunidad' (community), 'comunicar' (to communicate), 'comuna' (commune), and 'comunión' (communion). All these words carry the core meaning of sharing or having something in common with others.

Many English words are related to 'común' through the same Latin ancestor 'communis', including 'common', 'community', 'communicate', 'communion', and 'commune'. The connection is easy to see both in spelling and meaning - all these words involve the idea of sharing or joining together. Even the word 'municipal' (relating to a city or its government) is distantly related, as it comes from the same Latin 'munis' (duty, service) that forms part of 'común'.