Slang term for a white man, originating, according to a comment in the book "Beneath the underdog" by Charles Mingus, (not verbatim)
"A white man looking for a prostitute in early 20th Century Harlem who, because he didn't want to get out of his car to call a girl, he just honked to get the girls attention"
I think this is the most plausible definition.
"You hear that honky over there? He wants you, baby"