Definitions:

1. Implies a festive or joyful atmosphere and can be used to describe both an emotional state and the ambiance of a particular event or setting. NOUN
   • The room was filled with the gaiety fo the holiday season.
2. Refers to the state or quality of being lighthearted, cheerful, or full of high spirits. NOUN
   • Her gaiety was infectious, making everyone around her smile.

Synonyms:

• cheerfulness
• exuberance
• joviality
• Joyfulness
• merriment