Fidget terribly, being talented (6)
I believe the answer is:
gifted
'talented' is the definition.
(synonyms)
'fidget terribly' is the wordplay.
'terribly' indicates an anagram.
'fidget' with letters rearranged gives 'GIFTED'.
'being' acts as a link.
(Other definitions for gifted that I've seen before include "Possessed of natural talent" , "Exceptionally clever" , "exceptional talent" , "Talented, having great natural ability" , "Brilliant" .)