The Collaborative International Dictionary of English v.0.48:
Buncombe \Bun"combe\, Bunkum \Bun"kum\, n. [Buncombe a county of
Speech-making for the gratification of constituents, or to
gain public applause; flattering talk for a selfish purpose;
anything said for mere show. [Cant or Slang, U.S.]
All that flourish about right of search was bunkum --
all that brag about hanging your Canada sheriff was
bunkum . . . slavery speeches are all bunkum.
To speak for Buncombe, to speak for mere show, or
Note: "The phrase originated near the close of the debate on
the famous `Missouri Question,' in the 16th Congress.
It was then used by Felix Walker -- a na["i]ve old
mountaineer, who resided at Waynesville, in Haywood,
the most western country of North Carolina, near the
border of the adjacent county of Buncombe, which formed
part of his district. The old man rose to speak, while
the house was impatiently calling for the `Question,'
and several members gathered round him, begging him to
desist. He persevered, however, for a while, declaring
that the people of his district expected it, and that
he was bound to `make a speech for Buncombe.'" --W.