the.com/idler
A person doing nothing with great commitment, or a wheel that spins purely to keep things in line.
means Either someone habitually lazy, or a gear or pulley that guides a belt without driving anything itself.
from From Old English idel, meaning empty or worthless, the same root that gives us idle — a word for both vacant lots and vacant afternoons.
Mechanical jobIdler gears guide and tension, transmit no useful power.
Engine idleSame root: a motor running but going nowhere.
Literary fansSamuel Johnson wrote essays under the title The Idler.