Challenging difference

Both "reto" and "desafio" are nouns that mean "challenge." What is the distinction between them? Which one would be used in a courtly or duel context? I would guess that disafio is the one related to a duel or a similar challenge. This word is an obvious cognate of "defy" or "defiance." Someone once told me that no two English words have exactly the same meaning or set of connotations. Another person told me that, when it comes to different languages, there's little in the way of exact equivalence of meanings.