Cloudy nuclear explosion (7)
I believe the answer is:
unclear
'cloudy' is the definition.
(I've seen this in another clue)
'nuclear explosion' is the wordplay.
'explosion' is an anagram indicator.
'nuclear' with letters rearranged gives 'UNCLEAR'.
(Other definitions for unclear that I've seen before include "Indistinct" , "in clouds?" , "Not easy to grasp" , "Not certain" , "Not distinct in nuclear way" .)