Fabulous animal (7)
I believe the answer is:
unicorn
'fabulous animal' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for unicorn that I've seen before include "Legendary one-horned horse" , "Fabulous beast like horned horse" , "Imaginary white horse with long horn" , "Fabulous animal like horse with horn" , "Imaginary one-horned creature" .)