Immature fuss on the French perfume (10)
I believe the answer is:
adolescent
'immature' is the definition.
(similar in meaning)
'fuss on the french perfume' is the wordplay.
'fuss' becomes 'ado' (synonyms).
'on' means one lot of letters go next to another.
'the french' becomes 'le' ('the' in French).
'perfume' becomes 'scent' (synonyms).
'ado'+'le'+'scent'='ADOLESCENT'
(Other definitions for adolescent that I've seen before include "juvenile" , "Teenager" , "Immature" , "Youth" , "Teenage" .)