BUT

but [buht; unstressed buht]
–conjunction
on the contrary; yet: My brother went, but I did not.
–adverb
only; just: There is but one God. (more about this one later)
–noun
buts, reservations or objections: You'll do as you're told, no buts about it.
—Idioms
but for, except for; were it not for: But for the excessive humidity, it might have been a pleasant day.

Origin:
bef. 900; ME buten, OE būtan for phrase be ūtan on the outside, without. See by, out