Where does “but” come from?

But comes from Old English būtan, a preposition whose original sense remains uncertain.

but (English): Apart from, except , excluding; Outside of;...

Definitions

Step	Language	Word	Meaning
1	Middle English	but	Alternative form of bote
2	Old English	būtan	without, outside of, except, only; outside of
3	Proto-West Germanic	*biūtan	—