the number of steps of descent from the same ancestor that bar two related people from marrying
禁止通婚的亲等
a thing that is desired all the more because it is not allowed
禁果
used to express a fervent wish that something does not happen
上帝（天）不容（表达不希望发生某事的强烈愿望）
[with clause]God forbid that this should happen to anyone ever again.
上帝不容这类事在任何人身上重演。