Praiseworthy officer holding key to energy (9)
I believe the answer is:
admirable
'praiseworthy' is the definition.
(I've seen this before)
'officer holding key to energy' is the wordplay.
'officer' becomes 'admiral' (admiral is a kind of officer).
'holding' indicates putting letters inside.
'key' becomes 'b' (eg B major, musical key).
'to' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mcd).
'admiral' going around 'b' is 'admirabl'.
'admirabl'+'e'='ADMIRABLE'
(Other definitions for admirable that I've seen before include "Praiseworthy" , "Deserving of praise" , "Deserving respect and approval" , "Deserving of esteem" , "Worthy of being held in high opinion" .)