Smart way to reduce energy (4)
I believe the answer is:
cute
'smart' is the definition.
(I've seen this before)
'way to reduce energy' is the wordplay.
'way' becomes 'cut' (cut is a kind of way).
'to reduce' indicates taking the first letters (I've seen 'reduced' mean this (the word is reduced to its first letter)).
The initial letter of 'energy' is 'e'.
'cut'+'e'='CUTE'
(Other definitions for cute that I've seen before include "Small, delightful" , "Charming, quaint" , "Quaintly attractive" , "Quaintly pleasing" , "Attractive and quaint (4" .)