Real Dictionary

nuclear winter
Nuclear winter refers to the possible effects on the environment of a war in which large numbers of nuclear weapons are used. It is thought that there would be very low temperatures and very little light during a nuclear winter.

nuclear winter in American English
a hypothetical condition following nuclear war in which light from the sun is cut off by clouds of smoke and dust resulting in very low temperatures and consequent devastation of the environment and loss of life
noun: the general devastation of life, along with worldwide darkness and extreme cold, that some scientists believe would result from a global dust cloud screening out sunlight following large-scale nuclear detonations

nuclear winter in British English
noun: a period of extremely low temperatures and little light that, it has been suggested, would occur as a result of a nuclear war