Medicine with smudged date on it (8)
I believe the answer is:
antidote
'medicine' is the definition.
(antidote is a kind of medicine)
'smudged date on it' is the wordplay.
'smudged' indicates an anagram (the letters are smudged or messed up).
'date'+'on'+'it'='dateonit'
'dateonit' is an anagram of 'ANTIDOTE'.
'with' is the link.
(Other definitions for antidote that I've seen before include "Medicine acting against a poison" , "It counteracts poison" , "Counteracting medicine" , "Counter-measure" , "Counterpoison" .)