Axe tree down to earth (4)
I believe the answer is:
fire
'axe' is the definition.
(both can mean to dismiss or sack)
'tree down to earth' is the wordplay.
'tree' becomes 'fir' (fir tree is a kind of tree).
'down to' is a charade indicator (letters next to each other) (joining in a down clue).
'earth' becomes 'E'.
'fir'+'e'='FIRE'
(Other definitions for fire that I've seen before include "Manually operated device for dealing with flames" , "Blaze - sack" , "Weaponry" , "Sack; conflagration" , "Set light to; shoot" .)