Family member, about fifty, in French article (5)
I believe the answer is:
uncle
'family member' is the definition.
(brother of a parent)
'about fifty in french article' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'fifty' becomes 'l' (Roman numeral).
'in' is an insertion indicator.
'french article' becomes 'une' (indefinite article in French).
'c'+'l'='cl'
'cl' placed inside 'une' is 'UNCLE'.
(Other definitions for uncle that I've seen before include "Family relation" , "One receiving pawn" , "Law enforcement body" , "Pawnbroker's nickname" , "Pawnbroker (sl.)" .)