Beanie certainly hides relation (5)
I believe the answer is:
niece
'relation' is the definition.
(I know that niece is a type of kinswoman)
'beanie certainly hides' is the wordplay.
'hides' indicates the answer is hidden within the clue.
'NIECE' can be found hidden inside 'beanie certainly'.
(Other definitions for niece that I've seen before include "Criminal" , "Brother's girl" , "Family girl" , "Preparation for curdling milk" , "Brother or sister's daughter" .)