The Spanish word 'muro' comes directly from the Latin word 'murus', which meant 'exterior wall'. The word has maintained both its form and meaning remarkably well over time, with only a minor change from the Latin '-us' ending to the Spanish '-o' ending, which is a common pattern in Spanish words derived from Latin.

Some related Spanish words include 'muralla' (city wall or rampart), which is derived from the same Latin root and represents a more specific type of wall, and 'murar' (to wall up or fortify), which is a verb formed from 'muro'.

While English 'wall' comes from a different Germanic root, there are several English words related to the Latin 'murus'. These include 'mural' (a painting on a wall), 'immure' (to enclose within walls), and 'intramural' (situated or occurring within the walls of a building). The word 'demure' also comes from Latin 'de muro' meaning 'from the wall', originally referring to someone who was modest and reserved, as if staying close to the walls.