By such methods it was found possible to bring about an enormous diminution of vocabulary. Given, for instance, the word good, there was no need for such a word as bad, since the required meaning was equally well — indeed, better — expressed by ungood. All that was necessary, in any case where two words formed a natural pair of opposites, was to decide which of them to suppress. Dark, for example, could be replaced by unlight, or light by undark, according to preference.

https://orwell.ru/library/novels/1984/english/en_app