Nah, it's one of those things that's best left vague. It keeps it suitably... grandiose. Clearly defining it as "bravery and battle cunning" or whatever other definition saps it of some of its power, makes it more ordinary. It becomes no different than a goes-to-the-bravest Green Lantern power ring, which works perfectly for a sci-fi concept like Green Lantern but not as well with the whole gods-and-the-unknowable approach. And I wouldn't say it counts as Designated Hero, which is for characters who are "presented as heroic, doesn't really do anything heroic." Marvel's Thor is clearly a big, damn hero, so one doesn't find worthiness on his part hard to accept.