Gaslight [...]

From the Wikipedia article:

Gaslight is an American 1944 mystery-thriller film, adapted from Patrick Hamilton's 1938 play Gas Light, about a woman whose husband slowly manipulates her into believing that she is going insane. The 1944 version was the second version to be filmed, following the British film Gaslight, directed by Thorold Dickinson and released in 1940. This 1944 version was directed by George Cukor and starred Ingrid Bergman, Charles Boyer, Joseph Cotten, and 18-year-old Angela Lansbury in her screen debut. Gaslight had a larger scale and budget than the earlier film, and lends a different feel to the material. To avoid confusion with the first film, this version was originally given the title The Murder in Thornton Square in the UK.

"To gaslight" someone is to manipulate someone psychologically, making them feel as though they are losing their sanity.