Crossword Genius

Doctor at no harm in the long run (8)

Ross

I believe the answer is:

marathon

'the long run' is the definition.
(long-distance run)

'doctor at no harm' is the wordplay.
'doctor' is an anagram indicator.
'at'+'no'+'harm'='atnoharm'
'atnoharm' with letters rearranged gives 'MARATHON'.

'in' acts as a link.

(Other definitions for marathon that I've seen before include "no easy task" , "Race; battle" , "The longest foot race in sport" , "26-mile foot race" , "Long distance race" .)

I've seen this clue in The Sun.
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