Where does “buten” come from?

buten (Middle English) comes from Old English būtan, from Proto-West Germanic *biūtan — outside, externally.

Ancestry of “buten”, step by step

StepLanguageWordMeaning
1Old Englishbūtanwithout, outside of, except, only; outside of
2Proto-West Germanic*biūtanoutside, externally
Every word from Proto-West Germanic *biūtan →Every word from Old English būtan →