The Spanish word 'mulo' (meaning 'male mule') comes directly from the Latin word 'mulus', which had the same meaning. This is a straightforward inheritance from Latin to Spanish, with minimal changes in form and no change in meaning. A mule, being the offspring of a female horse and a male donkey, has been an important working animal throughout history in both Roman and Spanish cultures.

The Spanish word 'mula' (female mule) is closely related to 'mulo', being simply the feminine form of the same word. You might also encounter 'mulero' (mule driver) or 'mulada' (group of mules), which are derived from the same root.

While English 'mule' might look slightly different from Spanish 'mulo', they are indeed related words, both ultimately coming from Latin 'mulus'. The English word was borrowed through Old French 'mul'. Understanding this connection can help you remember that 'mulo' refers to the same animal in Spanish.