Invisible nun wandering around diocese (6)
I believe the answer is:
unseen
'invisible' is the definition.
(similar in meaning)
'nun wandering around diocese' is the wordplay.
'wandering' indicates anagramming the letters.
'around' indicates putting letters inside.
'diocese' becomes 'see' (both can mean a cathedral area).
'nun' anagrammed gives 'unn'.
'unn' enclosing 'see' is 'UNSEEN'.
(Other definitions for unseen that I've seen before include "Concealed" , "Passage for translation" , "Not noticed" , "Unobserved" , "Lurking" .)