Noun

(uncountable)  The state of being happy.

* {{quote-book, year=1963, author=(Margery Allingham)

, title=(The China Governess) , chapter=2 citation , passage=Now that she had rested and had fed from the luncheon tray Mrs. Broome had just removed, she had reverted to her normal gaiety .  She looked cool in a grey tailored cotton dress with a terracotta scarf and shoes and her hair a black silk helmet.}}

(countable)  Merrymaking or festivity.