Khorne isn't about killing. "Killing" is not an emotion. Physical decay is certaintly not an emotion, you can SEE it.
All the killing and rotting are symptoms of the emotion(s) which drive each god.
You can't be rage incarnate without acting on it and slaughtering things. You can't be despair incarnate without causing it somehow.
You can argue for a specific word although most are just synonyms, or if there are secondary emotions mixed in.
Hope is just opposite to Nurgle's being though, there is no hope against incurable disease or aging. Is nurgle being hope actually supported in any warhammer related writing anywhere? I wouldn't have thought that this MASSIVE BOOK OF CHAOS LORE I have right here would be fairly authoritative? I'm just paraphrasing GW's stuff in my arguments here you see.
A more interesting discussion would be getting THE emotion or set of emotions right for each god as there are so many similar words...