The Spanish word 'intestinal' comes from the Latin word 'intus' meaning 'inside' or 'within'. This developed into the Latin adjective 'intestinus' meaning 'internal'. The Spanish noun 'intestino' (intestine) comes directly from this Latin word, and when combined with the Spanish adjective suffix '-al', it forms 'intestinal', meaning 'relating to the intestines'.

A simpler related Spanish word is 'intestino' (intestine), which is the noun form without the adjectival suffix. This word is more commonly encountered in basic Spanish vocabulary when discussing anatomy or medical topics.

English speakers will recognize the cognate words 'intestine' and 'intestinal', which share the same Latin origin. The English words maintained nearly identical spelling and meaning to their Spanish counterparts. Another related English word is 'internal', which also derives from Latin 'intus' (inside), showing how the same root developed to describe things that are on the inside or within something else.