Cur in among relatives (7)
I believe the answer is:
mongrel
'cur' is the definition.
(I know that cur can be written as mongrel)
'in among relatives' is the wordplay.
'in' indicates a hidden word.
'MONGREL' is hidden in the letters of 'among relatives'.
(Other definitions for mongrel that I've seen before include "of mixed blood" , "mixed stock" , "Dog of mixed breed" , "Non-pedigree" , "of unknown variety" .)