Description of explosive reaction that could be more than cruel! (13)
I believe the answer is:
thermonuclear
'description of explosive reaction' is the definition.
The definition and answer are not the same part of speech.
'could be more than cruel' is the wordplay.
'could be' indicates an anagram.
'more'+'than'+'cruel'='morethancruel'
'morethancruel' with letters rearranged gives 'THERMONUCLEAR'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for thermonuclear that I've seen before include "Like reactions inside stars and some weapons" , "As some bombs" , "Like atomic weapons" , "H- (as in H-bomb)" .)