Serious enjoyment cycling by a French city (7)
I believe the answer is:
unfunny
'serious' is the definition.
(thesaurus)
'enjoyment cycling by a french city' is the wordplay.
I cannot quite understand how this works, but
'enjoyment' could be 'fun' (enjoyable activities) and 'fun' is present in the answer.
'city' could be 'ny' (short for New York) and 'ny' is found within the answer.
'a french' could be 'un' ('a' in French) and 'un' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for unfunny that I've seen is " Not amusing".)