Fire-breathing monster (7)
I believe the answer is:
chimera
'fire-breathing monster' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for chimera that I've seen before include "Lion-headed monster" , "Mythological animal; something illusory" , "A wild fancy" , "Wild or impossible idea" , "Mythical creature; delusion" .)