Mechanical part, maybe on a bridge (3)
I believe the answer is:
cam
'a bridge' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'mechanical part maybe on' is the wordplay.
'mechanical' becomes 'ca' (I can't justify this - if you can you should believe this answer much more).
'part' indicates taking the first letters.
'on' means one lot of letters go next to another.
The first letter of 'maybe' is 'm'.
'ca'+'m'='CAM'
Can you help me to learn more?
(Other definitions for cam that I've seen before include "River of eastern England" , "Rotating projection; river" , "River also called Granta" , "University city's river" , "running through university city?" .)