The nacelle (pron.: /nəˈsɛl/ nə-SELL) is a cover housing (separate from the fuselage) that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the function of a conventional fuselage. The covering is typically aerodynamically shaped.
Other uses 
- Science fiction: In the Star Trek series, it is used to describe the parts of a starship containing the propulsive components of a ship's warp drive. Specifically, the two (or more) nacelles house the warp field coils, which generate a warp field when fed high energy plasma supplied by the warp reactor, located elsewhere in the ship.
- Edward Turner used the term to describe his styling device introduced in 1949 to tidy the area around the headlamp and instrument panel of his Triumph Speed Twin, Thunderbird and Tiger 100 motorcycles. This styling device was much copied within the British industry thereafter, although Czech motorcycle manufacturer CZ were using it beforehand. Indeed, the Royal Enfield Bullet still retains their version, the 'casquette', on their current models. The last Triumphs to sport nacelles were the 1966 models of the 6T Triumph Thunderbird 650, 5TA Triumph Speed Twin 500, and 3TA Triumph Twenty One 350.
- The Triumph Owners' Motor Cycle Club calls its monthly magazine 'Nacelle'. This is named after the Triumph styling device designed by Edward Turner.
- Name for the generator and gearbox "shell" on a horizontal axis wind turbine (HAWT).
Like many aviation terms, the word comes from French, in this case from a word for a small boat.