The Word is:”but”

but1

/bʌt,bət/
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.AUSTRALIAN/NZSCOTTISH  informal
(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”

Source credit: Google