As far as one can go in a race (8)
I believe the answer is:
distance
'as far as one' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'can go in a race' is the wordplay.
I cannot quite see how this works, but
an anagram of 'can' is 'anc' which is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for distance that I've seen before include "Space between two places" , "Ascend it from one point to another" , "league, for example" , "Length between two points" , "Interval between two points" .)