IPA: /ˈkɑːrtɒp/
KK: /ˈkɑrˌtɑp/
This word describes something that is made to be carried on the roof of a vehicle, like luggage or a boat.
We used a cartop carrier to transport our kayak to the lake.
The word 'cartop' is formed from 'car' (from Old English *carr*, meaning a wheeled vehicle) and 'top' (from Old English *top*, meaning the highest point or upper part). The word 'cartop' refers to the upper part or roof of a wheeled vehicle.
Think of the 'top' of a 'car' — that's what 'cartop' means, the upper part of a vehicle.