IPA: //ˈkɑːrˌdʒækər//
KK: /ˈkɑrˌdʒækər/
A person who steals a car while someone is inside it.
The police arrested a carjacker who took a vehicle at gunpoint.
Carjacker is formed from "car" (from Latin *carrus*, meaning a wheeled vehicle) and "jacker" (from the verb "jack" meaning to lift or raise, which in this context refers to stealing). The word describes someone who steals a car, typically by force or threat.
Think of someone who 'lifts' ('jacker') a 'car' — that's why a carjacker is someone who steals a car.