Definitions: (1) joyous and lively; happy and lighthearted <a gay song in your heart>; (2) given to a pleasurable social life <the gay spirit of Paris>; exuberant; high -spirited; (3) freedom from care; a contented state of mind
Derivation: Proto-Germanic, “lively, fast, quick”
Synonyms: blithe, sprightly
Observation: A good example of how words change over time.