International in a French running club (5)
I believe the answer is:
union
'club' is the definition.
(thesaurus)
'international in a french running' is the wordplay.
'international' becomes 'i' (abbreviation eg in IMF).
'in' means one lot of letters goes inside another.
'a french' becomes 'un' ('a' in French).
'running' becomes 'on' (I've seen this in other clues).
'un'+'on'='unon'
'i' put inside 'unon' is 'UNION'.
(Other definitions for union that I've seen before include "political alliance" , "The coming together of separate parts" , "See 22" , "Association - guild" , "Combination" .)