The Spanish word 'diablito' meaning 'little devil' comes from combining the word 'diablo' (devil) with the diminutive suffix '-ito'. The word 'diablo' itself has an interesting journey, tracing back through Latin 'diabolus' (devil) to the Ancient Greek 'diábolos', which originally meant 'slanderer' or 'accuser'. This Greek word was later adopted into Latin where it took on the more specific meaning of 'devil', and this meaning carried forward into Spanish.

The most obvious related Spanish word is 'diablo' (devil), which is the base word from which 'diablito' is formed. The suffix '-ito' is a very common Spanish diminutive that you'll see in many words to indicate something is small or endearing, like 'perrito' (little dog) from 'perro' or 'casita' (little house) from 'casa'.

In English, we can find related words like 'diabolical' (devilish or evil) and 'devil' itself, though 'devil' took a different path through Germanic languages rather than through Latin. The word 'diabolic' in English comes from the same Greek root 'diábolos' through Latin, just like the Spanish 'diablo' and 'diablito'.