It shows how far away the northeast is (9)
I believe the answer is:
milestone
'it shows' is the definition.
The definition suggests a singular noun which matches the answer.
'far away the northeast is' is the wordplay.
I cannot really understand how this works, but
'far' could be 'miles' (mile is a unit of distance) and 'miles' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'northeast' could be 'ne' (abbreviation) and 'ne' is present in the answer.
A single letter 'o' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'how' acts as a link.
Can you help me to learn more?
(Other definitions for milestone that I've seen before include "Significant stage of development" , "Roadside distance marker" , "Significant developmental stage" , "Pillar" , "Important stage (reached)" .)