The Spanish word 'estómago' (meaning 'stomach') traces its origins back to Ancient Greek. It began with the Greek word 'στόμα' (stoma) meaning 'mouth'. This evolved into the Greek word 'στόμαχος' (stomakhos), which meant both 'stomach' and 'gullet' - reflecting the connection between the mouth and the digestive system. The Greeks passed this word to Latin as 'stomachus', keeping the meaning of 'stomach'. Finally, when the word entered Spanish, it took on the form 'estómago', with the addition of the initial 'e-' (a common development in Spanish words borrowed from Latin that began with 's' + consonant) while maintaining the same meaning of 'stomach'.

While 'estómago' itself is a common Spanish word, there are related Spanish medical terms like 'estomatitis' (inflammation of the mouth) and 'estomatólogo' (mouth specialist/dentist), which share the same Greek root 'stoma' (mouth). These technical terms maintain a connection to the original meaning of the Greek root word referring to the mouth.

English speakers might recognize this connection in medical terms like 'stoma' (a surgical opening), 'stomatic' (relating to the mouth), and 'stomatology' (the study of the mouth). The word 'stomach' itself is also directly related, coming from the same Greek source 'stomakhos'. This shared etymology explains why 'estómago' and 'stomach' sound similar despite being in different languages.