A derogatory term that generally means "fool" or anything to that effect.
The latter, along with its other definition (which refers to a kind of bird), is defined in dictionary.com, but, due to the fact that it seems to possess the characteristics of a slang word, I felt that it would be useful if it was actually defined as a slang word.
In fact, it may have actually been an old English slang word, as an English person who I know was familiar with the term to a certain extent.
Also, it was used in a song in J.R.R. Tolkien's "The Hobbit" when Bilbo was trying to anger the giant spiders in the Mirkwood forest to lead them away so that he could rescue his companions.