We don't have synonyms for barguest yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are largest, baguet and bargest.
(n) :
Alternative spelling of barghest. [(mythology, British) A legendary monstrous black dog, said to possess large teeth and claws, and (sometimes) to be capable of changing form.]
(n) :
Alternative spelling of barghest. [(mythology, British) A legendary monstrous black dog, said to possess large teeth and claws, and (sometimes) to be capable of changing form.]