Industry vehicle (9)
I believe the answer is:
diligence
This might be a double definition.
'industry' is the first definition.
(synonyms)
'vehicle' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
Can you help me to learn more?
(Other definitions for diligence that I've seen before include "Careful and persistent work or effort" , "needing proper care and attention" , "Old stagecoach" , "hard effort" , "Thoroughgoing application" .)