Driller dies — TNT unstable (7)
I believe the answer is:
dentist
'driller' is the definition.
(a dentist might use a dental drill)
'dies tnt unstable' is the wordplay.
'unstable' indicates anagramming the letters.
'dies'+'tnt'='diestnt'
'diestnt' anagrammed gives 'DENTIST'.
(Other definitions for dentist that I've seen before include "Person qualified to treat teeth - tends it (anag)" , "One treating teeth" , "Tooth specialist" , "part of the medical team" , "Tooth doctor" .)