'blood-related' originates from the combination of 'blood' and 'related', where 'blood' refers to family lineage and 'related' means connected or associated.

'blood' and 'related' have been used in English since the Middle Ages, and their combination into 'blood-related' has been used to describe familial connections.

Initially, it meant 'connected by blood or lineage', and this meaning has largely remained the same in modern usage.