What word means the opposite of serious?

There are many words that could be considered the opposite of "serious," depending on the context. Here are some options:

General opposites:

* Lighthearted

* Humorous

* Frivolous

* Playful

* Casual

* Informal

* Relaxed

Opposites in specific contexts:

* Fun (opposite of a serious situation)

* Flippant (opposite of a serious attitude)

* Trivial (opposite of a serious matter)

* Unimportant (opposite of a serious issue)

* Whimsical (opposite of a serious tone)

* Silly (opposite of a serious demeanor)

The best word to use depends on the specific context and the nuance you want to convey.