Carriage jumped on by opportunist (9)
I believe the answer is:
bandwagon
'carriage' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'jumped on by opportunist' is the wordplay.
I cannot quite understand how this works, but
'on' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bandwagon that I've seen before include "Fashionable movement" , "latest trend" , "Suddenly fashionable cause or activity" , "vehicle for musicians" , "See 24" .)