Footbridge? (4)
I believe the answer is:
arch
'footbridge?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
This is the entire clue.
Can you help me to learn more?
(Other definitions for arch that I've seen before include "Curve that spans an opening" , "Curved aperture" , "Affectedly playful or extreme" , "Wellington's, perhaps" , "Embow" .)