Nuclear Meltdown. Noun. Slang for a severe nuclear reactor accident which is considered very serious because of the possibility that the reactor contaminant will be defeated, thus releasing the core's highly radiactive and toxic elements into the atmosphere and environment.

It is a testament to Natalie Portman's natural beauty that, even when dressed for an impending nuclear meltodwn, she still manages to look better than 98 percent of the people on the face of the soon-to-be-destroyed-by-a-long-nuclear-winter Earth.