Nacelle (n): An enclosure on an aircraft, (usually) separate from the fuselage. Commonly used to refer to the housing of an aircraft engine, but can also indicate a structure protecting equipment or crew. Different sources give the meaning as simply "the boatlike, enclosed body of an aeroplane", and the word can also be used to mean the body of an airship.
Originates from the Old French nacele, for 'small boat', which in turn comes from the Latin navicella, meaning 'small ship' (navis is Latin for 'ship').
Sources: The American HeritageŽ Dictionary of the English Language, Fourth Edition; Webster's Revised Unabridged Dictionary; dictionary.com