father-in-law

A parent-in-law is a person who has a legal affinity with another by being the parent of the other's spouse. Many cultures and legal systems impose duties and responsibilities on persons connected by this relationship. A person is a child-in-law to the parents of the spouse, who are in turn also the parents of those sibling-in-laws who are siblings of the spouse. Together, the members of this family affinity group are called the in-laws.