Gaiety is a noun for a attitude or atmosphere that is happy or lively, something with lots of energy. The plural is spelled gaieties. An alternative spelling is listed in US dictionaries as gayety, but this has been out of favor for decades and is only used now for proper nouns or in old quotes.
Outside the US a common phrase is the gaiety of nations. It means a sense of happiness or cheerfulness, and may sometimes be used ironically to mean the exact opposite.
Mirth can be a synonym for gaiety, but it is more specific in its definition. Mirth is the laughter or happiness that accompanies laughter.
The festival of Ganga Saptami, also known as Ganga Pujan or Ganga Jayanti, was celebrated with gaiety and fervour in Haridwar on Saturday. [The Tribune India]
While enjoying the gaieties, feel free to check out the train display, tour the mansion and check out each of the mansion’s Christmas trees — with a special surprise in store — Christmas Under the Sea! [The Delaware County Daily Times]
It further said that Low “has added to the gaiety of nations, and it has been estimated that over five million breakfast tables scattered about the world rock with mirth every morning when the daily newspaper is passed round.” [The Hindu]
This feeling of mirth just bubbling under everyone’s behaviour creates an air of expectancy – how will the person act out a scene you know is coming next? [IOL Tonight]