Energy hack not quite sound on reflection (4)
I believe the answer is:
echo
'sound on reflection' is the definition.
'echo' can be an answer for 'reflection' (echo is a kind of reflection). I'm not certain of the 'sound on' bit.
'energy hack not quite' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'hack' becomes 'chop' (synonyms).
'not quite' means to remove the last letter (most but not all of the word).
'chop' with its final letter taken off is 'cho'.
'e'+'cho'='ECHO'
Can you help me to learn more?
(Other definitions for echo that I've seen before include "One who slavishly copies" , "Reverberate - nymph spurned by Narcissus" , "Nymph (only able to repeat the last words of others)" , "Nymph whose love Narcissus spurned" , "repercussion" .)