The Spanish word 'toro' meaning 'bull' comes from the Latin word 'taurus', which also meant 'bull'. The Latin word itself can be traced back to Ancient Greek 'tauros' (ταῦρος), also meaning 'bull'. This is a great example of how some basic animal words have remained remarkably stable in their form and meaning across thousands of years and multiple languages in the Indo-European family.

The word 'toro' is already one of the most basic and common Spanish words for 'bull', so you're unlikely to encounter simpler related Spanish words. However, you might see it in compounds like 'torero' (bullfighter) or 'torear' (to bullfight), which are derived from 'toro'.

English speakers might recognize the connection to the word 'taurus', which comes from the same Latin source. This word is used in English both as the astrological sign (represented by a bull) and as a genus name for wild cattle. The word 'taurine' meaning 'relating to bulls' is another English derivative. These English words preserve the 'tau-' sound from the ancient Latin and Greek forms, while Spanish evolved to use 'to-' instead.