Mark initially can see hardly at all (8)
I believe the answer is:
scarcely
'hardly at all' is the definition.
('scarcely' can be a synonym of 'hardly at all')
'mark initially can see' is the wordplay.
'mark' becomes 'scar' ('scar' can be a synonym of 'mark').
'initially' indicates taking the first letters.
'see' becomes 'ely' (example where cathedral located in diocese).
The first letter of 'can' is 'c'.
'scar'+'c'+'ely'='SCARCELY'
(Other definitions for scarcely that I've seen before include "Barely, hardly" , "Surely not" , "Almost not" , "Only just or hardly even" , "Not quite" .)