Aircraft propeller! (3)
This clue could be a double definition.
'aircraft' is the first definition.
(jet is a kind of aircraft)
'propeller' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for jet that I've seen before include "Spurt of water or fast plane" , "Type of plane" , "Very black or fast plane" , "Hard black mineral or plane engine" , "Kind of plane, or a glossy black" .)
(Another definition for jet engine that I've seen is " Aircraft propulsion unit".)