What is a noun for gaily?

There isn't a single perfect noun for "gaily." However, depending on the context, you can use several options:

General gaiety:

* Gaiety - This is the most direct noun form of "gaily."

* Cheerfulness

* Joviality

* Merriment

* Lightheartedness

* Vivacity

* Briskness

* Liveliness

* Sprightliness

For specific instances of "gaily":

* If you're talking about a gaily decorated room, you could use decoration or adornment.

* If you're talking about a gaily dressed person, you could use attire or apparel.

The best option depends on the specific situation and the desired nuance.