Its anger dissipated, it won't react (5,3)
I believe the answer is:
inert gas
'it won't react' is the definition.
The definition suggests a singular noun which matches the answer.
'its anger dissipated' is the wordplay.
'dissipated' indicates anagramming the letters.
'its'+'anger'='itsanger'
'itsanger' anagrammed gives 'INERT GAS'.
Can you help me to learn more?
(Other definitions for inert gas that I've seen before include "Passive element in the helium group" , "Unreactive "noble" element, such as argon" , "Eg, helium or argon" , "Eg, helium, xenon etc." , "Such as neon or xenon" .)