Tuna-mad relation (4)
I believe the answer is:
aunt
'relation' is the definition.
(I know that aunt is a type of kinswoman)
'tuna-mad' is the wordplay.
'mad' indicates an anagram.
'tuna' is an anagram of 'AUNT'.
(Other definitions for aunt that I've seen before include "Family member" , "Blood relative" , "Tuna for the odd relative" , "Family relative" , "Put up with" .)