Which word is not a synonym for EARNEST sincere serious or riotous?

The word that is not a synonym for earnest, sincere, or serious is riotous.

Here's why:

* Earnest, sincere, and serious all describe a state of being genuine, heartfelt, and focused.

* Riotous describes something chaotic, wild, and disorderly, which is the opposite of the other three words.