Riviera city — home to European relation (5)
I believe the answer is:
niece
'relation' is the definition.
(I know that niece is a type of kinswoman)
'riviera city home to european' is the wordplay.
'riviera city' becomes 'nice' (I've seen this in another clue).
'home to' is an insertion indicator (some letters house or home others).
'european' becomes 'E' (abbreviation e.g. EU).
'nice' going around 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Family relation" , "Family relative" , "Daughter of a sibling" , "Brother's girl" , "Preparation for curdling milk" .)