Long distance runner, one in old women’s race (6)

I believe the answer is:

amazon

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'long distance runner' is the definition.
'Amazon' can be an answer for 'runner' (Amazon is an example). I am not sure about the 'long distance' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for amazon that I've seen before include "Mythic woman warrior" , "World's largest river" , "banker" , "Encourage, ask" , "Net giant" .)

I've seen this clue in The Times.

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