"We never really knew what to call each other," Ms. Oxhorn-Ringwood said. "When Evan was a kid, I would call Louise my ex-husband's new wife, but after 10 years I couldn't do that anymore. We came up with stepwives to describe the relationship between ex-wives and current wives."
Alex Witchel, "Wives No. 1 and No. 2 Bury the Sandals," The New York Times, May 12, 2002
Today's word is in the news because of a book called
Stepwives: 10 Steps to Help Ex-Wives and Stepmothers End the Struggle and Put the Kids First, by Louise Oxhorn and Lynne Oxhorn-Ringwood. The above citation hints that they coined the term, but that's not true. However, the earliest citation I could uncover for today's word isn't quite right, as you can see below.
In case you're wondering, the word stephusband the current husband of a man's ex-wife or the ex-husband of a man's current wife has made the occasional appearance in the media over the years. The earliest citation for this sense is from 1989.

We asked for specific phrases for adults to use instead of "boyfriend" and "girlfriend." Here are some of your suggestions: ... Nikki Klinsky "Stephusband" or "Stepwife."
Bob Greene, "It's a close call among old friends," Chicago Tribune, January 24, 1989
|
In our context, the woman must be a man's wife or ex-wife and not merely a girlfriend. So the honor of coining the term in its "correct" sense goes to writer Phyllis Stevens who published a novel called Stepwives in 1990.