The Spanish word 'eco' (meaning 'echo') comes from the Latin word 'echo', which in turn was borrowed from Ancient Greek 'ἠχώ' (echó), meaning 'sound' or 'echo'. This is a clear example of how some scientific and technical terms have remained remarkably stable in form and meaning as they passed from Greek through Latin into modern Romance languages.

The word 'eco' is relatively simple and common in Spanish already, but you might encounter it in compounds like 'ecología' (ecology) or 'ecosistema' (ecosystem), where 'eco-' functions as a prefix related to environment and natural systems.

English speakers will easily recognize the connection to the English word 'echo', which comes from the same Greek source. The words are not only related - they're virtually identical in both spelling and meaning! English also uses 'echo' in similar compound words like 'echolocation' and 'echography'. The prefix 'eco-' is also used similarly in both languages in words relating to the environment.