Gay

In English, the word's primary meaning was "joyful", "carefree", "bright and showy", and the word was very commonly used with this meaning in speech and literature. For example, the optimistic 1890s are still often referred to as the Gay Nineties. The title of the 1938 French ballet Gaîté Parisienne ("Parisian Gaiety"), which became the 1941 Warner Brothers movie, The Gay Parisian,10 also illustrates this connotation. It was apparently not until the 20th century that the word began to be used to mean specifically "homosexual", although it had earlier acquired sexual connotations.2

Usage statistics from English books, according to Google Ngram Viewer.
The word may have started to acquire associations of immorality as early as the 14th century, but had certainly acquired them by the 17th.2 By the late 17th century, it had acquired the specific meaning of "addicted to pleasures and dissipations",11 an extension of its primary meaning of "carefree" implying "uninhibited by moral constraints". A gay woman was a prostitute, a gay man a womanizer, and a gay house a brothel.122 An example is a letter read to a London court in 1885 during the prosecution of brothel madam and procuress Mary Jeffries that had been written by a girl while enslaved inside of a French brothel:

The use of gay to mean "homosexual" was often an extension of its application to prostitution: a gay boy was a young man or boy serving male clients.14

Person 1: I love you.
Person 2: Dude that's gay...