IPA: /ˈflætərər/
KK: /ˈflætərər/
A person who praises someone excessively, often to gain favor or advantage.
He was known as a flatterer, always complimenting the boss to get ahead at work.
Flatterer → It is formed from "flatter" (from Old French *flatter*, meaning to stroke or caress) and "-er" (meaning a person who). A flatterer is a person who strokes or praises someone excessively, often insincerely.
Think of someone who 'strokes' or 'praises' others to gain favor — that's what a flatterer does.