Definition: A ludicrously false statement. Basically it means BS or nonsense.
Analysis: Actually, you probably already know this word by its more common spelling: bunkum.
The origin of this word is fascinating. In 1819, a North Carolina congressman, the Honorable Felix Walker, was giving a rambling speech with little relevance to the current debate. He refused to yield the floor, and claimed that he wasn’t speaking for Congress but instead “for Buncombe” (a county in North Carolina he represented). That’s all it took.
Over time, the spelling changed to “bunkum,” and the meaning strangely changed to be “excellent.” Then it changed back in 1870, when a San Francisco gambler introduced a new game “banco” played with dice that were later found out to be loaded. Sure enough, BUNCO became known to mean swindle or cheat, and bunkum reverted back to its original meaning. (Source)
The word DEBUNK came directly from this: it’s just bunk(um) with the prefix de- (meaning to remove). link thanks to NeatoRama
We lived in NC for seven years, and I heard of this county often, but never made the connection. Don’t you just love how language evolves!?