What exactly does the phrase "all but" mean?

Question

For example, "all but ordinary" -- I've seen "all but" used in ways so that this could mean that something is simply ordinary, or that it is anything but ordinary. Which is it?

Answer 1

It means "that it is anything but ordinary".

"All but" is the same thing as "Everything except"

So if I said, "I'm all but ordinary." that means I'm very different, unordinary, and basically any word that doesn't mean ordinary.

Answer 2

'But' is most often a conjunction, but (lol) it may also be used as a preposition, where it means 'except'. Think about 'all but ordinary' meaning 'all EXCEPT ordinary.'