Race apt to make one perspire (4)
I believe the answer is:
heat
'race' is the definition.
(I know that heat is a type of race)
'apt to make one perspire' is the wordplay.
I cannot really see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
The remaining letters 'het' 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 heat that I've seen before include "High temperature" , "Energy that caues a rise in temperature" , "brings out a sweat?" , "Get agitated" , "Cook" .)