JFK sister-in-law (5)
I believe the answer is:
ethel
'jfk sister-in-law' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ethel that I've seen before include "- Barrymore, actress" , "Perhaps a Barrymore" , "chapel" , "Dame --- Smyth; William Brown's sister" , "Lady" .)