Precisely ten perform in cathedral city (7)
I believe the answer is:
exactly
'precisely' is the definition.
(synonyms)
'ten perform in cathedral city' is the wordplay.
'ten' becomes 'x' (roman numeral).
'perform' becomes 'act' (acting is a kind of performing).
'in' is an insertion indicator.
'cathedral city' becomes 'ely' (I've seen this before).
'x'+'act'='xact'
'xact' going into 'ely' is 'EXACTLY'.
(Other definitions for exactly that I've seen before include "how one might express agreement?" , "Indeed; verbatim" , "In every respect" , "in nice way" , "In precise terms" .)