Green’s Dictionary of Slang

(US) nonsensical.

1855		N.Y. Daily Trib. 26 Jan. 7/6: The Board of Aldermen consumed nearly two hours last evening in a buncombe debate.
1871		Sportsman (London) ‘Notes on News’ 5 Jan. 2/1: We are not surprised to find that the following day was devoted to ‘buncombe’ speech-making.