* Quiet: This is a general antonym for boisterous, implying a lack of noise or activity.
* Calm: This implies a state of peacefulness and tranquility, the opposite of boisterous excitement.
* Subdued: This suggests a restrained or muted atmosphere, the opposite of boisterous energy.
* Sedate: This implies a composed and dignified demeanor, the opposite of boisterous exuberance.
* Reserved: This implies a lack of outward enthusiasm or display of emotions, the opposite of boisterous expressiveness.
The best antonym for "boisterous" will depend on the specific situation and the nuance you want to convey.