Rewarding, if tedious, to keep skilful (6)
I believe the answer is:
gifted
'skilful' is the definition.
(thesaurus)
'rewarding if tedious to keep' is the wordplay.
'to keep' indicates a hidden word.
'GIFTED' is hidden in the letters of 'rewarding if tedious'.
(Other definitions for gifted that I've seen before include "Talented, having great natural ability" , "With high talent" , "Possessing natural talent" , "Exceptionally clever" , "especially intelligent" .)