Rudi Gernreich definitely named the monokini as a joke. If anyone doesn’t know the history, Louis Reard’s bikini was named after Bikini Atoll, the site of the first public nuclear test, because the tiny suit would create just as much of an explosion. Seriously. The fact that “bi” was in the name was just coincidence, but monokini and trikini and all the rest are backformed from the original.
We covered the monokini in Rudi Gernreich’s pubikini - This, I gotta see! I got a whole bunch of Popular Link badges from that thread.