Avengers shot invisible weapon (5,3)
I believe the answer is:
nerve gas
'invisible weapon' is the definition.
'nerve gas' can be an answer for 'weapon' (I've seen this before). I'm not certain of the 'invisible' bit.
'avengers shot' is the wordplay.
'shot' is an anagram indicator.
'avengers' is an anagram of 'NERVE GAS'.
Can you help me to learn more?
(Other definitions for nerve gas that I've seen before include "Poison" , "Chemical warfare agent" , "WW2 prison camp" , "Poisonous vapour" , "Type of weapon" .)