noun. A rodent unrelated by blood. And lost in the mists of time!
Real citation: "My ex step-ferret used to like to hang out inside the couch. She would come out if you shook a box of cereal because she loved Fruit Loops."
(Nov. 14, 2008, Snopes, http://message.snopes.com/showthread.php?t=38364)
Made-up citation: "I wish I could stop slithering back to my ex-step-ferret. But a soulmate is a soulmate..."