(possibly obsolete) happy, joyful, and lively.
Example: "The gay science"
Quick, fast.
(possibly obsolete) festive, bright, or colourful.
Example: "Pennsylvania dutch include the plain folk and the gay folk."
Sexually promiscuous (of any gender), (sometimes particularly) engaged in prostitution.
Homosexual:
A pejorative:
(of a dog's tail) upright or curved over the back.
(possibly obsolete) considerable, great, large in number, size, or degree.