IPA: /ˈklɒkə/
KK: /ˈklɑːkər/
A person who illegally changes the mileage on a car's odometer to make it seem like it has been driven less than it actually has.
The mechanic discovered that the clocker had tampered with the car's mileage.
Clocker is formed from "clock" (from Middle English *clokke*, meaning a device for measuring time) and "-er" (meaning a person who). A clocker is a person who uses or operates a clock, often in the context of timing events.
Think of a 'clock' as a device that measures time, and the '-er' indicates a person. So, a clocker is someone who works with or operates a clock.