IPA: /ˈtʃæstaɪzər/
KK: /ˈtʃæstaɪzər/
A person who criticizes or reprimands someone for their behavior or actions.
The teacher acted as a chastiser when she scolded the students for being late.
Chastiser → It is formed from "chastise" (from Old French *chastier*, meaning to punish or correct) and "-er" (meaning a person who). A chastiser is a person who punishes or corrects others.
Think of someone who 'corrects' or 'punishes' others — that's what a chastiser does.