Imaginary, fanciful (6)
I believe the answer is:
unreal
I believe this clue is a double definition.
'imaginary' is the first definition.
(similar in meaning)
'fanciful' is the second definition.
(similar in meaning)
(Other definitions for unreal that I've seen before include "Phantasmagorical" , "Artificial, insubstantial" , "Existing only in the imagination, not actual" , "Illusory; amazing" , "Dreamlike" .)