Resort detaining English kinswoman (5)
I believe the answer is:
niece
'kinswoman' is the definition.
(I know that niece is a type of kinswoman)
'resort detaining english' is the wordplay.
'resort' becomes 'nice' (French coastal resort).
'detaining' indicates putting letters inside.
'english' becomes 'E' (abbreviation).
'nice' enclosing 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Brother's girl" , "Family relation" , "Family girl" , "One of the family" , "Daughter of a sibling" .)