Formal:
* Escort: This emphasizes the act of accompanying someone, often for protection or social propriety.
* Attendant: This suggests someone who is present to provide assistance or supervision.
* Guardian: This emphasizes the responsibility for the safety and well-being of the person being chaperoned.
* Mentor: This suggests someone who provides guidance and support, often in a more informal setting.
Informal:
* Companion: This implies someone who accompanies another person for social purposes.
* Guide: This emphasizes the role of leading or directing the person being chaperoned.
* Supervisor: This suggests someone who oversees the activities of the person being chaperoned.
* Watcher: This emphasizes the act of observing and keeping an eye on the person being chaperoned.
The best synonym depends on the specific situation and the role the chaperone is playing.