but what

1. with the exception of; excepting; save [nobody came but me]: earlier, and still sometimes, regarded as a conjunction and followed by the nominative case [nobody came but I (came)]
2. except; other than: used with an infinitive as the object: we cannot choose but (to) stay

conjunction

1. and in spite of this; and even so; yet: he is a villain, but he has some virtues
2. and on the contrary: I am old, but you are young
3. unless; except that: it never rains but it pours
4. that: I don't question but you're correct
5. that . . . not: it's not so high but we can jump it

adverb

1. only: if I had but known
2. merely; no more than; not otherwise than: he is but a child
3. just: I heard it but now
4. on the other hand; yet: used to introduce a sentence
5. Slang absolutely; positively: he did it, but good

pronoun