Drunk and volatile, a dangerous chemical combination (4,9)
I believe the answer is:
high explosive
'a dangerous chemical combination' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'drunk and volatile' is the wordplay.
'drunk' becomes 'high' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'volatile' becomes 'explosive' (similar in meaning).
'high'+'explosive'='HIGH EXPLOSIVE'
Can you help me to learn more?
(Other definitions for high explosive that I've seen before include "Eg, gelignite" , "HE in full" .)