Hard stone over English cathedral city ... (6)
I believe the answer is:
steely
'hard' is the definition.
(similar in meaning)
'stone over english cathedral city' is the wordplay.
'stone' becomes 'st'.
'over' says to put letters next to each other.
'english' becomes 'e' (abbreviation).
'cathedral city' becomes 'ely' (English city with a cathedral).
'st'+'e'+'ely'='STEELY'
(Other definitions for steely that I've seen before include "Hard and metallic" , "Strong" , "Coldly determined" , "firm" , "Gimlet-eyed" .)