Can be ridden, though one may go on foot (4)
I believe the answer is:
mule
'can' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for mule that I've seen before include "Obstinate person?" , "Drug courier; animal" , "Hybrid animal - slipper" , "Crossbreed" , "Drug smuggler" .)