The Spanish word 'invierno' (meaning 'winter') comes from Old Spanish 'ivierno', which developed from the Latin adjective 'hibernum' meaning 'wintry' or 'of winter'. This Latin word was related to the noun 'hiems' meaning 'winter'. The evolution from Latin 'hibernum' to modern Spanish 'invierno' shows typical sound changes, including the addition of an 'n' (likely through dissimilation) and the preservation of the 'i' vowel sound.

The Spanish word 'hibernación' (hibernation) is a related term that comes from the same Latin root 'hibernum'. While 'invierno' refers to the season itself, 'hibernación' refers to the winter sleep that some animals undergo during this cold season.

English speakers might recognize the connection to words like 'hibernate' and 'hibernation', which come from the same Latin root 'hibernum'. Just as 'invierno' relates to winter in Spanish, these English words specifically relate to the winter dormancy of animals. The scientific term 'hibernaculum' (a winter shelter for dormant animals) also shares this etymology.