Fabulous creature (7)
I believe the answer is:
unicorn
'fabulous creature' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for unicorn that I've seen before include "Fabulous beast like horned horse" , "fabulous thing to behold" , "Fabulous one-horned animal" , "Imaginary, horned horse-like creature" , "Team of three" .)