Explosive device in mint awfully close at hand (8)
I believe the answer is:
imminent
'close at hand' is the definition.
'explosive device in mint awfully' is the wordplay.
'explosive device' becomes 'mine' (mine is a kind of explosive device).
'in' indicates putting letters inside.
'awfully' indicates anagramming the letters.
'mint' is an anagram of 'imnt'.
'mine' put within 'imnt' is 'IMMINENT'.
(Other definitions for imminent that I've seen before include "About to happen very soon" , "Likely to occur at any moment" , "Likely to happen at any moment" , "now expected" , "Approaching fast" .)