The Spanish word 'anónimo' (meaning 'anonymous') comes from Latin 'anonymus', which was borrowed from Ancient Greek 'anonymos' meaning 'nameless'. The Greek word was formed by combining two elements: the prefix 'an-' meaning 'without' and 'onoma' meaning 'name'. So literally, the word was built to mean 'without a name'.

This construction follows a common pattern in Greek where 'an-' (or 'a-' before consonants) is used to create words expressing the absence or lack of something. The meaning has remained remarkably stable throughout its journey from Greek through Latin to Spanish, consistently referring to something or someone whose name is unknown or withheld.

A related Spanish word is 'nombre' (meaning 'name'), which, while not directly derived from the Greek 'onoma', serves as a helpful reminder that 'anónimo' refers to something without a name. The prefix 'an-' appears in other Spanish words like 'analfabeto' (illiterate, literally 'without alphabet') and 'anormal' (abnormal, 'without normality'), following the same pattern of indicating absence.

The English word 'anonymous' is a direct cognate of Spanish 'anónimo', as both descend from the same Greek source. English has preserved many words with the same Greek 'an-' prefix, such as 'anarchy' (without ruler), 'anaesthetic' (without feeling), and 'anomaly' (without regularity). The element 'onoma' is preserved in English words like 'onomatopoeia' (literally 'name-making', referring to words that sound like what they describe) and 'synonym' (literally 'with the same name').