There's nothing persistent in this scent (5)
I believe the answer is:
odour
'this scent' is the definition.
(synonyms)
'there's nothing persistent' is the wordplay.
'there's nothing' becomes 'o' (I've seen this in other clues).
'persistent' becomes 'dour' (I can't justify this - if you can you should believe this answer much more).
'o'+'dour'='ODOUR'
'in' is the link.
Can you help me to learn more?
(Other definitions for odour that I've seen before include "Any property detected by the olfactory system" , "Nasty smell" , "Olfactory sensation" , "for the nose to detect" , "Pong" .)