Secondly, the Lord prohibits sexual relationships between those who are related by blood but belong to the extended family. This includes grandchildren (Leviticus 18:10) and aunts (Leviticus 18:12–13). Wenham calls this, second-degree consanguinity.
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10 You shall not uncover the nakedness of your son’s daughter or of your daughter’s daughter, for their nakedness is your own nakedness.