O que significa but ?

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conjunction

1.

used to introduce a phrase or clause contrasting with what has already been mentioned.

"he stumbled but didn't fall"

synonyms:yet; More

2.

used to indicate the impossibility of anything other than what is being stated.

"one cannot but sympathize"

synonyms:(do) other than, otherwise than, except

"one cannot but sympathize"

preposition

1.

except; apart from; other than.

"we were never anything but poor"

synonyms:except (for), apart from, other than, besides, aside from, with the exception of, short of, bar, barring, excepting, excluding, omitting, leaving out, save (for), saving; 

informaloutside of

"everyone but him had gone"

adverb

1.

no more than; only.

"he is but a shadow of his former self"

synonyms:only, just, simply, merely, no more than, nothing but; More

2.

INFORMAL•AUSTRALIAN/NZ

(used at the end of a sentence) though; however.

"he was a nice bloke but"

noun

1.

an argument against something; an objection.

"no buts —just get out of here"