It helps the wheels go round (3)
I believe the answer is:
oil
This clue could be a double definition.
'it helps the wheels' is the first definition.
The definition suggests a singular noun which matches the answer.
'round' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'go' is the link.
Can you help me to learn more?
(Other definitions for oil that I've seen before include "Type of fuel" , "SECOND PART OF 23" , "what can be seen on iceberg" , "Lubricant or petroleum" , "Liquid fuel" .)