dipstick

[ dip-stik ]
/ ˈdɪpˌstɪk /

noun

a rod for measuring the depth of a liquid; especially, a thin metal rod used to measure the oil level in the crankcase of an automotive engine.
Slang. fool; jerk.

Origin of dipstick

First recorded in 1925–30; dip1 + stick1

British Dictionary definitions for dipstick

dipstick
/ (ˈdɪpˌstɪk) /

noun

a graduated rod or strip dipped into a container to indicate the fluid level
British slang a fool