It can be used as an adverb, a noun, or even a preposition.
Preposition: With the exception of; except; save:
No one replied but me.
Noun: Buts, reservations or objections:
You'll do as you're told, no buts about it.
Adverb: Only; just:
There is but one God.
This three letter word holds the power to change everything and lie to ourselves.
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