Grave letters about Yorkshire city (5)
I believe the answer is:
ripon
'yorkshire city' is the definition.
(city in Yorkshire)
'grave letters about' is the wordplay.
'grave letters' becomes 'rip' (I've seen this in another clue).
'about' becomes 'on' (as in a book 'on' a certain topic).
'rip'+'on'='RIPON'
(Other definitions for ripon that I've seen before include "northern town" , "North Yorkshire cathedral city" , "see" , "N. Yorks market town" , "Yorks cathedral" .)