Who is the "hamw" mentioned in the Hadith "Al-Hamw is death," and is it permissible for the daughter's wife to be in seclusion with him?

The meaning of "al-hamw" (the in-law) in the noble Prophetic tradition is a non-mahram (definition) relative of the husband, such as his brother, paternal uncle, brother's son, and paternal uncle's son. It is forbidden to enter upon non-mahram women. "Al-hamw is death" means that seclusion with the brother's wife, or similar relatives, is more dangerous than seclusion with a non-mahram woman because people tend to be lenient in such situations.

There is no objection to the daughter's husband secluding himself with his wife's mother. However, the brother's son's wife is not a mahram, and it is not permissible for her to seclude herself with a non-mahram.