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The act of manipulating someone psychologically so that they begin to doubt their experience of reality. The phrase comes from the 1938 play Gas Light, in which the protagonist attempts to induce insanity in his wife by constantly questioning or doubting her reports of strange events, such as the dimming of the house's gas lights (which has in fact occurred and is related to the husband's nefarious activities). Her husband must be gaslighting her because she suddenly doubts all the evidence that she's found of his indiscretions. The administration has been accused of gaslighting with its repeated attempts to spread disinformation.