Cousins-in-Law
In an anthropology class long ago, the teacher told us that the aboriginal people of Australia were apalled by the ignorance of the English, when it came to names of family relationships. Dozens of relationships that had specific names in their own language were rendered into English as "cousin". As genealogists we are often more specific. I can say "Gordon is my third cousin, once removed.", but that doesn't say which family line we have in common. So I might say, "Gordon is my third cousin, once removed on my Buchanan line."

I recently found out that Gordon's wife is the first cousin of my friend Fran. If I describe my family connection to Fran as a "cousin-in-law", I think most people would get the general idea. (i.e. There is no blood relationship between Fran and me, but we are connected through the marriage of our cousins.)

In the same way, the mother of my friend Donna is the sister to my uncle Charlie's wife. There is no blood relationship between Donna and me, although we share an uncle and aunt.

Wikipedia says that Gordon's wife is my cousin-in-law, but Fran is not, nor is Donna. Hmm ...
http://en.wikipedia.org/wiki/Cousin#Cousin-in-law

Maybe the lengthy explanations are best after all.