Appealing to reduce energy (4)
I believe the answer is:
cute
'appealing' is the definition.
(I've seen this in another clue)
'reduce energy' is the wordplay.
'reduce' becomes 'cut' (synonyms).
'energy' becomes 'e' (physics symbol as in E=mc2).
'cut'+'e'='CUTE'
'to' acts as a link.
(Other definitions for cute that I've seen before include "Location" , "Endearing" , "Shrewd" , "Smart" , "Charming, quaint" .)