Vehicle it is illegal to leave in the street (6)
I believe the answer is:
litter
'vehicle' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'it is illegal to leave in the street' is the wordplay.
I cannot really see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
The remaining letters 'lier' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for litter that I've seen before include "Trash left lying about" , "dropped by a new dam, perhaps?" , "Family" , "Do the kittens create rubbish?" , "Discarded rubbish" .)