The word “but” is used as -

but – conjunction হিসেবে সবচেয়ে বেশি ব্যবহৃত হলেও এটি Preposition, Adverb, Pronoun হিসেবেও ব্যবহৃত হতে পারে।
Everyone but Jamil was present. (without অর্থে Preposition)
Life is but a walking shadow. (only অর্থে Adverb)
There is no mother but loves her child. (who not অর্থে Pronoun)