They get engaged in the car (5)
I believe the answer is:
gears
'car' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for gears that I've seen before include "Sarge (anag.)" , "Rages (anag.)" .)