Ace (6)
'ace' is the definition.
(both can mean a master of something)
This is the entire clue.
(Other definitions for expert that I've seen before include "Skilled workman or specialist" , "One has specialist knowledge or ability" , "One practised" , "Authority" , "Masterly" .)
'ace' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fabulous that I've seen before include "Legendary or informally marvellous" , "almost incredible" , "Marvellous, incredibly great" , "Smashing" , "Out of this world" .)