Tincture of opium (8)
I believe the answer is:
laudanum
'tincture of opium' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for laudanum that I've seen before include "Former painkiller" , "Opiate popular in Victorian times" , "Opium-based drug" , "Tincture of opium" , "Coleridge took this" .)