Similar words
demônio
Worth distinguishing: diabo often refers to THE devil/Satan specifically; demônio is more general, for any evil spirit.
Similar in other languages
German
Teufel
Teufel is the German word for the same thing — both mean "devil."
Spanish
diablo
diablo is the Spanish word for the same thing — both mean "devil."
Practice
1 What does diabo mean?
devil
2 Fill the gap: Que ___ é isso?
Full sentence: Que diabo é isso? (What the devil is that?)
3 Which fingerprint chart matches diabo?
diabo: neutral register, common frequency, general domain, negative connotation.