barghest
Barghest (noun) means a huge black dog from old folk tales, said to have fierce teeth and claws and sometimes the power to change shape.
Etymology
The word was probably inherited from Northern Middle English *berghgast, *barghgast, itself from bergh, bargh (“barrow”) plus gast (“ghost”). Some have suggested the first element is instead burgh (“town”) or bere (“bear”), but these alternatives lack semantic motivation.