Alleviation of pain (6)
I believe the answer is:
relief
'alleviation of pain' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for relief that I've seen before include "Lightening of a burden" , "Assistance given to people in need" , "Cosmos" , "A lessening of pressure" , "Easement from pain or distress" .)