The Spanish word 'medio' meaning 'middle' or 'half' comes directly from the Latin word 'medius', which had the same meaning. This is a straightforward inheritance from Latin to Spanish, with the word maintaining both its form and core meaning remarkably well over time.

Several common Spanish words share this Latin root, including: 'mediano' (medium-sized), 'mediodía' (noon/midday), and 'medianoche' (midnight). The prefix 'medi-' in Spanish often carries the sense of 'middle' or 'half' in compound words.

English has many cognates that come from the same Latin root 'medius', including 'medium', 'median', 'mediate', and 'intermediate'. The word 'middle' itself, while Germanic in origin, is distantly related to the same Indo-European root. Even 'Mediterranean' literally means 'middle of the earth' using this same Latin root 'medi-'.