IPA: /ˈreɪdə/
KK: /ˈreɪdər/
A person who attacks a place or group in a sudden and violent way, often to steal or cause damage.
The raider quickly escaped with the stolen goods before anyone could react.
Raider → It is formed from "raid" (from Old French *raide*, meaning a sudden attack) and "-er" (meaning a person who). A raider is a person who engages in a sudden attack or incursion into a place.
Think of someone who is involved in a 'sudden attack' ('raid') — the '-er' just means a person. A raider is someone who attacks suddenly.