Agree with artist, it’s a fanciful dream (7)
I believe the answer is:
chimera
'a fanciful dream' is the definition.
(chimera can mean a dream or fantasy)
'agree with artist' is the wordplay.
'agree' becomes 'chime'.
'with' says to put letters next to each other.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'chime'+'ra'='CHIMERA'
'it's' acts as a link.
(Other definitions for chimera that I've seen before include "figment of the imagination" , "phantom" , "Wild notion" , "fabulous creature" , "fantasy" .)