If nuke is "delete/hide," then what is "delete?"

"Delete" is like "dead", except that the posts aren't visible even if you have showdead turned on. We don't ever delete things unless users ask us to—typically because the window for deleting their own post has expired—and then only when they have a good reason for asking. Otherwise HN's bias is toward preserving history.

Coincidentally, I posted something else about "delete" a few hours ago: https://news.ycombinator.com/item?id=7975137.

What does "dead" mean?

dead posts are hidden by default. I believe once you have enough kamra there is a "showdead" option you can enable in your preferences. Dead posts/comments will be marked as [dead], but you can at least still see them.

"dead" on HN is like locking and hiding a thread -- no more voting or commenting and the thread disappears.