Hill to the west in Manhattan, say, within reach (6)
I believe the answer is:
nearby
'within reach' is the definition.
(thesaurus)
'hill to the west in manhattan' is the wordplay.
'hill' becomes 'brae' (Scottish term for a hill).
'to the west' says the letters should be written backwards (letters written right to left or 'east to west').
'in' is an insertion indicator.
'manhattan' becomes 'ny' (I can't justify this - if you can you should give a lot more credence to this answer).
'brae' in reverse letter order is 'earb'.
'earb' going into 'ny' is 'NEARBY'.
'say' is the link.
Can you help me to learn more?
(Other definitions for nearby that I've seen before include "somewhere close" , "Barney (anag)" , "Around the corner" , "Adjacent" , "[OPPOSITE OF] miles away" .)