It just means half so there is a chance Wolfie is called Dimidius, however he was never called that in the show (he was called a 'werewolf' or 'half vampire, half werewolf' I think). Dimidius might only be used impersonally by high ranking/old vampires or it might be used for half-humans only.
In context, vampires have a predator-prey relationship with humans and an antagonistic relationship with werewolves. Because they view humans and werewolves differently it seems likely that they'd have different words.
Who knows what the writers would have come up with given several more series. I would have liked to have seen more of Wolfie. :)