Energetic CID holds many back (7)
I believe the answer is:
dynamic
'energetic' is the definition.
(associated in meaning)
'cid holds many back' is the wordplay.
'holds' indicates putting letters inside.
'back' says the letters should be written in reverse.
'cid' placed around 'many' is 'cimanyd'.
'cimanyd' backwards is 'DYNAMIC'.
(Other definitions for dynamic that I've seen before include "Vigorous and effective" , "Energetic, with great force of character" , "Very active" , "Vigorous and go-ahead" , "Powerful and vigorous" .)