Malachy McCourt, actor, writer and brother of writer Frank, had a radio show on WMCA in New York City in the 1970's. At that time the word "gay" was just beginning to be known to the general public as "homosexual" - and Malachy didn't think that it was appropriate. He said something like, "I'm gay - but I do not have, or want to have, sex with other men!".

Now it's gotten stuck with other meanings such as "stupid".

Original definitions:

1. [a] bright and pleasant; promoting a feeling of cheer; "a cheery hello"; "a gay sunny room"; "a sunny smile".

Websterâ??s Dictionary, 1913:

Gay
<XPAGE=616 Gay (?), a. [Compar. Gayer (?); superl. Gayest.] [F. gai, perhaps fr. OHG. ghi swift, rapid, G. gäh, jäh, steep, hasty; or cf. OHG. whi beatiful, good. Cf. Jay.]

1. Excited with merriment; manifesting sportiveness or delight; inspiring delight; livery; merry.
Belinda smiled, and all the world was gay. Pope.
Gay hope is theirs by fancy fed. Gray.
2. Brilliant in colors; splendid; fine; richly dressed.
Why is my neighbor's wife so gay? Chaucer.
A bevy of fair women, richly gay In gems and wanton dress. Milton
3. Loose; dissipated; lewd. [Colloq.] Syn. -- Merry; gleeful; blithe; airy; lively; sprightly, sportive; light-hearted; frolicsome; jolly; jovial; joyous; joyful; glad; showy; splendid; vivacious.