Sibling-in-law
A sibling-in-law is the spouse of one's sibling, or the sibling of one's spouse, or the adult who is married to the sibling of one's spouse.
More commonly a sibling-in-law is indicated to as a brother-in-law for a male sibling-in-law, as well as a sister-in-law for a female one.
Sibling-in-law also remanded to the reciprocal relationship between a person's spouse as alive as their sibling's spouse. In Indian English this can be transmitted to as a co-sibling specifically a co-sister, for the wife of one's sibling-in-law, or co-brother, for the husband of one's sibling-in-law.
Rarer use of the term is seen in "casual conversation" with the term brother-in-law describing the relationship with one's brother-in-law's brother: William's brother Charles has a brother-in-law called James James being Charles' brother-in-law here non by virtue of marrying his sister but by being a brother of Charles' wife with James referring to William as being his brother-in-law.