Briefly try to pour scorn on source of irritation (4,4)
I believe the answer is:
heat rash
'source of irritation' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'briefly try to pour scorn' is the wordplay.
'briefly' means to remove the last letter.
'try' becomes 'hear' ('hear' can be a synonym of 'try').
'to pour scorn' becomes 'trash' (I can't justify this - if you can you should give a lot more credence to this answer).
'hear' with its final letter taken away is 'hea'.
'hea'+'trash'='HEAT RASH'
'on' acts as a link.
Can you help me to learn more?
(Other definitions for heat rash that I've seen before include "skin complaint" , "Irritating inflammation of sweat glands" , "Itching of the skin, caused by humid hot weather" .)