A guy who has had the misfortune to either be born with one testicle, or has had one gonad removed at some point in his life due to illness, accident, surgery or another tragic reason.
It is widely believed that Adolf Hitler himself was someone who possessed a solo bollock. Hence the song: "Hitler has only got one ball; the other is in the Royal Albert Hall . . ."
Matt: Do you fancy coming round to mine tonight, I'm going have a barbeque, seeing as the weather is nice?
Pecket: Sure,sounds good, who else is going to be there?
Matt: Well only Gled so far, but I've yet to ring round everyone else.
Pecket: Hitlers coming?
Matt: Who's Hitler?
Pecket: Gled's called Hitler, cos he only has one bollock!