Author, one making correction, by sound of it (6)
I believe the answer is:
writer
This might be a double definition.
'author' is the first definition.
('writer' can be a synonym of 'author')
'one making correction by sound of it' is the second definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
Can you help me to learn more?
(Other definitions for writer that I've seen before include "See 1, 12, 15, 23 across and 3, 6, 9 down" , "Novelist" , "Quiller" , "See 4" , "Author; correspondent" .)