Is the husband of your wife’s sister your brother-in-law?
I would have said “no” and been pretty sure I was reflecting standard usage, but it turns out I would have been wrong. Bill Poser at the Log has a post about this, sparked by “a news item in which men in this situation (one of whom is accused of trying to hire an assassin to kill the other) were described as brothers-in-law”; he was surprised to see it, because to him “there is no named relationship” between such men. I agreed with him, but he and I are in a distinct minority; most of the (so far) 74 comments say things like (to take the first two) “I use brother-in-law in that context, as does my wife” and “It never occurred to me not to use ‘brother-in-law’ to refer to my wife’s sister’s husband.” I thought perhaps it was a generational thing, since Webster’s Seventh New Collegiate Dictionary has the definition “broadly : the husband of one’s spouse’s sister,” whereas the entry in the newest (eleventh) edition drops the “broadly” and just includes “the husband of one’s spouse’s sister” as one of the basic senses, but I asked my wife and she has no problem with the broad sense. Furthermore, in the Log thread, Jerry Friedman (November 20, 2009 @ 3:14 am) said, “This has come up on alt.usage.english a few times, and the results are much like those here—everything from people who’ve never heard the extended sense to people who thought everyone used it. I don’t recall any regional pattern ever showing up.”
So I thought I’d ask you all the question I began with; you might add, for scientific purposes, where you’re from (or, if different, what dialect you speak), and (if, of course, you feel like it) your approximate age.
Incidentally, this problem does not arise in Russian, where there is a separate word свояк [svoyák] meaning ‘wife’s sister’s husband.’ And Sravana (November 20, 2009 @ 12:18 am) wrote in the Log thread, “In Indian English, Edward and Michael are co-brothers,” a term that (like prepone) might usefully be adopted by the standard language.