Gaslight and gaslighting

In recent times the words 'gaslight' and 'gaslighting' have become prominent in particular in the United States, aided by the efforts of Donald Trump and his cult followers, who want to believe that the truth is a lie.

The Google Books Ngram Viewer (see below) is a search engine that charts word frequencies from a large number of books and for the two words here the time period is 1938-2019. Gaslight has more frequencies than gaslighting.

The Merriam-Webster dictionary defines gaslighting as "psychological manipulation of a person usually over an extended period of time that causes the victim to question the validity of their own thoughts, perception of reality, or memories and typically leads to confusion, loss of confidence and self-esteem, uncertainty of one's emotional or mental stability, and a dependency on the perpetrator."

Whether it is gaslight, gaslit, gaslighter or gaslighting, M-W says "The Historical Dictionary of American Slang' has a record of use in a speech from 1956 in which a woman defines gaslight in a way that reflects the above definition and gives its source [as being a 1944 movie.] The term is commonly used today as a verb and verbal noun."