They tread on the road (5)
I believe the answer is:
tyres
'they' is the definition.
Both the definition and answer are plural nouns.
Perhaps there's an association between them I don't understand?
'tread on the road' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in 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 tyres that I've seen before include "Rubber wheel covers" , "Wheel coverings" , "Wheel hoops" , "rubber rings" .)