Geoff at Language Log has a post on Bilateral cross cousins. There's a word irrbanbin in Bardi, which refers to two sisters marrying two brothers (which is what happened on my father's side, to my father's mother and father, and their sister and brother respectively, with the result that my father has a number of bilateral cross cousins). The Bardi word is either an inalienably possessed noun or a verb (the irr- portion of the word is either 3pl present or 3pl possessive, you can't tell). I don't actually have any way to tell at present, and the only speaker of Bardi I asked who knew this word has now passed away. If it's a noun, the only way you'd be able to tell is by the 2sg or 3sg form, and this word doesn't take singular marking (I did ask that). If it's verb, I guess the only way you'd be able to tell is if it could take future marking. I assumed it was a noun at the time. It's time to go back to the field notes for that day to see if I got any more examples that didn't make it into the dictionary supplement. Moral of the story: always talk about your family with your consultants.