The Spanish colloquial term 'pompis' (meaning 'buttocks') has an interesting etymology that traces back to ancient Greek through Latin. It derives from the Spanish word 'pompa' (meaning 'pomp, ostentation'), which came from Latin 'pompa' (meaning 'procession, pomp'). The Latin term originated from Ancient Greek 'πομπή' (pompē), which meant 'procession' or 'escort'.

The semantic shift from 'procession/pomp' to 'buttocks' likely developed as a humorous euphemism, possibly relating to the prominent or ostentatious nature of that part of the anatomy. This kind of playful evolution in meaning is common in colloquial terms for body parts.

A closely related Spanish word is 'pompa', meaning 'pomp' or 'ostentation'. While 'pompis' took on a colloquial anatomical meaning, 'pompa' retained its original sense of ceremonial splendor or grandeur. You might hear 'pompa y circunstancia' as the Spanish equivalent of the English phrase 'pomp and circumstance'.

English speakers might recognize the connection to words like 'pomp', 'pompous', and 'pomposity', all of which derive from the same Greek and Latin roots. While the Spanish 'pompis' took an informal anatomical meaning, these English relatives maintained the sense of ceremonial display or excessive self-importance. For example, someone who is 'pompous' displays an exaggerated sense of self-importance or dignity.