Nerve gas makes a chap a goner, unfortunately (5,6)
I believe the answer is:
agent orange
'nerve gas' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'a chap a goner unfortunately' is the wordplay.
'chap' becomes 'gent' (I've seen this in other clues).
'unfortunately' is an anagram indicator.
'a'+'goner'='agoner'
'agoner' anagrammed gives 'orange'.
'a'+'gent'+'orange'='AGENT ORANGE'
'makes' acts as a link.
Can you help me to learn more?
(Other definitions for agent orange that I've seen before include "killer in Vietnam" , "Poisonous chemical" , "Dangerous chemical" , "What defoliates" , "A herbicide" .)