The Spanish word 'diablo' (meaning 'devil') comes from Latin 'diabolus', which was borrowed from Ancient Greek 'διάβολος' (diabolos), meaning 'slanderer' or 'accuser'. The Greek word was formed by combining two elements: 'dia-' meaning 'through, across' and 'ballein' meaning 'to throw'. So literally, the original Greek word meant someone who 'throws across' accusations or slander. Over time, this meaning evolved from a general 'accuser' to specifically refer to the ultimate spiritual adversary - the devil.

The word 'diablo' is quite fundamental in Spanish and doesn't have many simpler related forms. However, you might encounter variations like 'diabólico' (diabolical) or 'endiablado' (devilish), which are derived from 'diablo'.

English speakers can easily remember 'diablo' by connecting it to several similar English words that share the same Greek origin: 'devil' (though this followed a different evolutionary path through Germanic languages), 'diabolical' (evil or devilish), and 'diabolic'. The word 'diabetes' also shares the Greek prefix 'dia-' (meaning 'through'), though it combines with a different root.