gay

First recorded in 1275–1325; Middle English gai, from Old French “happy, cheerful,” from Germanic; compare Old High German gāhi “fast, sudden”

The sexual orientation meaning of the word gay has become so predominant that people hesitate to use the term in its original senses of “merry, lively” and “bright or showy.” But the word's association with sexuality is not new. The word gay has had various senses dealing with sexual conduct since the 17th century. A gay woman was a prostitute, a gay man a womanizer, a gay house a brothel. This sexual world included gay men too, and gay as an adjective in the sexual meaning goes back at least to the late 1930s. After World War II, as social attitudes toward sexuality began to change, gay was applied openly by gay men to themselves, first as an adjective and later as a noun. It is no longer considered slang. Today, the noun often designates only gay men and is usually used as a collective plural: gays and lesbians. How do gays feel about this? But usage as a singular noun is usually perceived as insulting.
It has been argued that gay in the sense “awkward, stupid, or bad” is independent of the sexual sense, and therefore not homophobic. This argument is weakened by the fact that the sexual meaning has long been the dominant one, and thus permeates all usages of gay. See also homosexual.

Words like gay and lesbian are often used as umbrella terms describing anyone who experiences same-gender attraction, and also as more specific labels. Umbrella usage, as in gay marriage or lesbian couple, typically refers to any same-gender pairing, or to any person who is attracted to people of their own gender. Gay itself can also be used as an even more general term describing people of all genders who are attracted to their own gender.
As more specific labels, gay and lesbian often mean exclusive attraction to the same gender, and may be used in contrast with terms like bisexual. And gay can also be used to refer to only men who are attracted to men (exclusively or not), in contrast to lesbian, which only refers to women. Other terms, such as sapphic for women, are sometimes used to be unambiguously inclusive of people attracted to multiple genders.

C13: from Old French gai, from Old Provençal, of Germanic origin

Gayness is the word used to refer to homosexuality. The noun which refers to being carefree and merry is gaiety