Key worker climbing fiery mountain (4)

I believe the answer is:

etna

I'm a little stuck... Click here to teach me more about this clue!

'fiery mountain' is the definition.
'Etna' can be an answer for 'mountain' (Etna is an example). I am not certain of the 'fiery' bit.

'key worker climbing' is the wordplay.
'key' becomes 'e' (musical key).
'worker' becomes 'ant' (worker is a type of ant).
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'ant' in reverse letter order is 'tna'.
'e'+'tna'='ETNA'

Can you help me to learn more?

(Other definitions for etna that I've seen before include "Volcano in Italy" , "burning mountain" , "Explosive type" , "hotly-tipped runner" , "it may produce steam and ash" .)

I've seen this clue in The Sun.

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