A family related by blood (4)
I believe the answer is:
Here is my best explanation:
'related by blood' is the definition.
'a family' is the subsidiary indication.
'family' becomes 'kin' ('kin' can be a synonym of 'family').
(Other definitions for akin that I've seen before include "Of similar character", "Similar in character", "It's related", "Related by blood", "Like or related.", "Similar in quality", "Of like nature or related", "Related or similiar", "Of a similar nature" and "Having similar characteristics".)