In which horses race endlessly, then short burst and it's all over, having just one race (8)
I believe the answer is:
purebred
'in which horses race endlessly then short burst and' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?
'all over having just one race' is the wordplay.
I cannot quite understand how this works, but
'all' could be 'pure' (I've seen this in another clue) and 'pure' is located in the answer.
'over' could be 're' and 're' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'it's' acts as a link.
Can you help me to learn more?
(Another definition for purebred that I've seen is " Of unmixed race".)