Laces a gin cocktail relieving pain (9)
I believe the answer is:
analgesic
'relieving pain' is the definition.
(I've seen this before)
'laces a gin cocktail' is the wordplay.
'cocktail' is an anagram indicator.
'laces'+'a'+'gin'='lacesagin'
'lacesagin' with letters rearranged gives 'ANALGESIC'.
(Other definitions for analgesic that I've seen before include "Anodyne" , "number" , "medicament" , "A medicine used to relieve pain" , "Acting to relieve pain" .)