It dispels pain sir (7)
I believe the answer is:
aspirin
'it dispels pain sir' is the definition.
The definition suggests a singular noun which matches the answer. I also know that 'pain' relates to this answer.
'it dispels pain sir' is the wordplay.
'pain sir' can be anagrammed to 'ASPIRIN'.
But, I'm not sure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for aspirin that I've seen before include "Pain-relief drug" , "Anodyne" , "Common pain tablet" , "headache cure" , "Anti-inflammatory drug" .)