All my life, I've been vaguely aware that there's something about the word duo-tang that I was missing. It seemed like such an odd English word. Then, the other day, my daughter brought one home and the meaning hit me: duo = 2, tang = tongue-like projection (you can see three of them in the photo below).
It seems like I'm not the only one to miss the meaning. Here's a "duo-tang" with not a tang in sight. I suppose, though, that you can forgive the company its expanding use of a brand name.