fairing
Synonym discussion
Sense: noun/4
A fairing is a shaped cover whose job is to smooth airflow or water flow around part of a machine. Cowling is close, but it is especially common for the fitted cover around an engine or front section of an aircraft or motorcycle. Shroud is broader and can mean any protective covering, even when drag is not the main point. Panel is the everyday general word for a flat or curved piece on the outside, but it does not automatically suggest a streamlined design. Compare: a cracked fairing under a plane, the engine cowling on a small aircraft, a plastic fan shroud, and a side panel on a scooter.
Etymology
This engineering noun grew out of the English verb fair, which can mean shaping parts so they fit smoothly together. In modern technical use, a fairing is the shaped covering added to a vehicle or machine to make the outside line smoother and reduce drag.