Energy worker climbing fiery mountain (4)
I believe the answer is:
etna
'fiery mountain' is the definition.
'Etna' can be an answer for 'mountain' (Etna is an example). I'm unsure of the 'fiery' bit.
'energy worker climbing' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mcn).
'worker' becomes 'ant' (worker is a type of ant).
'climbing' is a reversal indicator (in a down clue, letters climb up).
'ant' back-to-front is 'tna'.
'e'+'tna'='ETNA'
Can you help me to learn more?
(Other definitions for etna that I've seen before include "source of fumes?" , "Neat kind of European volcano" , "Sicilian hothead?" , "A feature of Sicily" , "A neat sort of volcano" .)