Swear nothing left the racetrack (5)

I believe the answer is:

curse

I'm a little stuck... Click here to teach me more about this clue!

'swear' is the definition.
(I know that swear can be written as curse)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for curse that I've seen before include "Cause of harm or misery" , "Evil spell - oath" , "Profanity" , "Utter obscenities" , "Profane or obscene expression" .)

I've seen this clue in The Irish News.

Want a hint initially instead of a full solution? Install my app