Example sentence:
"As the concert ended, the atmosphere was all but ecstatic."
Replace words with synonyms:
- all = everything
- but = except
The sentence would appear:
"...the atmosphere was everything except ecstatic."
Meaning, "the concert was not ecstatic". It was all feelings except ecstatic.
I regularly hear similar sentences used in the way where "all but" means the exact opposite of my interpretation. The last straw of "curiosity : need-to-know" ratio broke when I heard it used in Band of Brothers--which very clearly implied the use of "all but" as a similar meaning to "very".
There's undoubtedly a hole in my logic.
Edit:
Band of Brothers quote: "He was just one more casualty in a war that was supposed to be all but over."