Just ran into the term "Gegenschwager" in an old civic record from Alsace. I have heard the term used before colloquially. It describes the relationship between A and D. where A married B, C married D, B and C are siblings, and A and D are not blood-related. It seems an archaic term (possibly of regional usage only), and my internet searches have not brought up any useful translation. (To clarify: A and C are brother-in law /sister- in-law, and the same goes for B and D. A and D are in-laws by proxy, so to speak.) Is there an English term for this relationship?