Explain this to me...?

Question

Here's the example:

The dark circles under his eyes all but vanished.

Does "all but" mean they did vanish? It makes it sound like they hadn't. :/

Answer 1

It means it mostly faded but some remain

Answer 2

It means they did everything except vanish.  Vanishing is the only thing left to do and they will probably vanish soon.

Opticians work on eyesight not dark circles.  Stupid sarcastic answer.

Answer 3

dark circles?? sounds like he needs to see an optician.

Answer 4

No, it means they faded to the point of almost having vanished, but were still there, barely.