Foolishly, I name a cathedral city (7)
I believe the answer is:
inanely
'foolishly' is the definition.
(synonyms)
'i name a cathedral city' is the wordplay.
'name' becomes 'nan' ().
'a cathedral city' becomes 'ely' (I've seen this before).
'i'+'nan'+'ely'='INANELY'
(Other definitions for inanely that I've seen before include "Stupidly" , "Senselessly" , "in a daft way" , "Vapidly" , "In a fatuous manner" .)