The story
From passenger + compartment.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: The part of a road vehicle partitioned from the engine compartment, trunk or boot, etc., designed to hold the passengers and usually the driver; but in limousines and some taxis, buses and goods vehicles, the driver is separated in a cab or driver's compartment. Full definition →
From passenger + compartment.
Etymology from Wiktionary, CC BY-SA 4.0.