The Spanish word 'estadio' (meaning 'stadium') comes from the Latin word 'stadium', which meant both a unit of length measurement and a race course. The Latin term was borrowed from Ancient Greek 'stadion' (στάδιον), which similarly referred to both a fixed unit of measurement and a race course where athletic competitions were held. The original Greek stadion was a measure of approximately 600 feet, and the running tracks built to this length eventually gave their name to the larger sporting venues we know today as stadiums.

While 'estadio' itself is a commonly used Spanish word, there aren't many simpler or more common Spanish words directly related to it etymologically. However, you might encounter related words like 'estadístico' (statistical) or 'estado' (state), though these actually come from different Latin roots.

The English word 'stadium' is a direct cognate of Spanish 'estadio', coming from the same Latin root 'stadium'. The main difference is that Spanish added an 'e-' at the beginning of the word (a common practice called prosthesis that Spanish often applies to words beginning with 's' + consonant). You might also recognize this root in words like 'stage' and 'stance', which evolved from the same concept of a measured or fixed standing place.