Bearing an exploded mine (4)
I believe the answer is:
mien
'bearing' is the definition.
(synonyms)
'an exploded mine' is the wordplay.
'an exploded' is an anagram indicator.
'mine' anagrammed gives 'MIEN'.
(Other definitions for mien that I've seen before include "Person's bearing" , "Dignified manner" , "Counterance - mine?" , "(One's) manner, bearing" , "Comportment" .)