Some steelyard in cathedral city (3)
I believe the answer is:
ely
'cathedral city' is the definition.
(English city with a cathedral)
'some steelyard in' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'ELY' is hidden in the letters of 'steelyard in'.
(Other definitions for ely that I've seen before include "Cambs diocese" , "English cathedral city" , "Cathedral city in East Anglia" , "See" , "Cathedral city in Cambridgeshire" .)