The Spanish word 'papi' (meaning 'daddy' as a term of endearment) comes from 'papa' combined with the Spanish diminutive suffix '-ito' (shortened to '-i'). 'Papa' itself can be traced back to Latin 'pāpa' (meaning 'father, papa'), which ultimately derives from Ancient Greek 'páppas' (πάππας), also meaning 'daddy' or 'papa'. This is a great example of how terms of endearment for fathers have remained remarkably similar across many centuries and different languages.

The most obvious related Spanish word is 'papa', which simply means 'dad' or 'daddy'. While 'papa' is the basic form, 'papi' adds an extra layer of affection through the diminutive ending. This is similar to how English speakers might use 'daddy' instead of 'dad' as a more affectionate term.

English speakers will recognize the similarity to words like 'papa' and 'pop/pops', which are also informal or affectionate terms for father. These words share the same ancient origin as the Spanish terms, demonstrating how some basic family words can remain similar across different languages. The repeated 'pa' sound is thought to come from the natural babbling sounds that babies make, which is why similar words for 'father' appear in many languages worldwide.