I typed gay into the dictionary that comes with ubuntu and got this:
Gay Gay (g[=a]), a. [Compar. Gayer; superl. Gayest.] [F.
gai, perhaps fr. OHG. g?hi swift, rapid, G. g[aum]h, j[aum]h,
steep, hasty; or cf. OHG. w?hi beatiful, good. Cf. Jay.]
[1913 Webster]
1. Excited with merriment; manifesting sportiveness or
delight; inspiring delight; livery; merry.
[1913 Webster]
Belinda smiled, and all the world was gay. --Pope.
[1913 Webster]
Gay hope is theirs by fancy fed. --Gray.
[1913 Webster]
2. Brilliant in colors; splendid; fine; richly dressed.
[1913 Webster]
Why is my neighbor's wife so gay? --Chaucer.
[1913 Webster]
A bevy of fair women, richly gay
In gems and wanton dress! --Milton.
[1913 Webster]
3. Loose; dissipated; lewd. [Colloq.]
Syn: Merry; gleeful; blithe; airy; lively; sprightly,
sportive; light-hearted; frolicsome; jolly; jovial;
joyous; joyful; glad; showy; splendid; vivacious.
[1913 Webster]
-- From The Collaborative International Dictionary of English v.0.48
I also looked in my Concise Oxford dictionary where it is defined as:
1 light-hearted and carefree, mirthful
2 characterised by cheerfulness or pleasure
3 brightly coloured, showy, brilliant
4
colloq homosexual
5
colloq dissolute, immoral
Madrake quotes
wordnet with much the same definitions