why they use "but" like that

[Uranium]

hello, everybody
i want to know what is the meaning of "human... they are but stubborn and foolish"
why he used "but" in the sentence
i want to know how to use "but" like that
other examples
i am but dust.
there are but one sun, one moon,...
thanks in advance

[Beeesneees]

It is an emphasis = an adverb which means 'only' or 'no more than'
He is but a shadow of his former self.

Possible synonyms
only, merely, just, solely, barely, alone, simply
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Cheers m' dears!

[Uranium]

thanks you very much
your reply make me so clear