Energy worker back to find volcano (4)
I believe the answer is:
etna
'volcano' is the definition.
(Mount Etna)
'energy worker back' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'worker' becomes 'ant' (worker is a type of ant).
'back' shows that the letters should be reversed in order.
'ant' in reverse letter order is 'tna'.
'e'+'tna'='ETNA'
'to find' is the link.
(Other definitions for etna that I've seen before include "Threatening mountain" , "smoker in Sicily" , "Volcanic mount in Sicily" , "Active European volcano" , "Highest peak in Italy south of the Alps" .)