all but

Almost, nearly, as in I've all but finished the book. This expression was used by Andrew Marvell in "Thoughts in a Garden": "Society is all but rude, To this delicious solitude." [Late 1500s]

The adverb has one meaning:

Meaning #1: (of actions or states) slightly short of or not quite accomplished; `near' is sometimes used informally for `nearly' and `most' is sometimes used informally for `almost'
  Synonyms: about, just about, almost, most, nearly, near, nigh, virtually, well-nigh