About Virginia Bobbitt Transue — born 10/12/40 (a month after me) — the wife of a brother (Bill) of my husband-equivalent (Jacques). More succinctly, my husband’s brother’s wife, in effect my sister-in-law-in-law. Or, putting it in more abstract terms, my spouse’s sib’s spouse, my sib-in-law-in-law.
Here we have the equivalence of X’S SPOUSE’S SIB’S SPOUSE to X’S SPOUSE’S SIB (my brother-in-law’s wife treated as my sister-in-law) — an equivalence not recognized by some people, while for other people, it’s routine. It’s the way things work for Virginia and me; I refer to her as my sister-in-law, she refers to me as her brother-in-law.
There are other equivalences. The point of all of them is not merely selecting simple terms: the equivalences express feelings of familial closeness, caring, and even responsibility; they are emotionally potent.
Another double in-law equivalence (distinct from the Arnold-Virginia relationship, though parallel to it): of X’S SIB’S SPOUSE’S SIB to X’S SIB’S SPOUSE, again in effect X’s sib-in-law-in-law. For example, Keene Daingerfield’s wife Elizabeth (Libby) Walcutt Daingerfield’s sister Ann Walcutt Winn’s husband Jack Winn — Keene’s sister-in-law’s husband — treated by Keene as his brother-in-law.
Now, the background to all of this. (Some of this will be a bit repetitious; I’m trying to pull out some really cool abstract distinctions that take a while to appreciate, because what we know about them is pretty much all below the level of our consciousness, and we don’t learn anything about kinship relations in school.)