Meaning

adverb and nothing more

originFrom Middle English but, buten, boute, bouten, from Old English būtan (“without, outside of, except, only”), from Proto-West Germanic *biūtan, *biūtini, equivalent to be- + out. Cognate with Scots but, bot (“outside, without, but”), Saterland Frisian buute (“without”), West Frisian bûten (“outside of, apart from, other than, except, but”), Dutch buiten (“outside”), Dutch Low Saxon buten…

Etymology from Wiktionary, CC BY-SA 3.0