Sole; merely (4)
I believe the answer is:
I believe this clue is a double definition.
'sole' is the first definition.
(I know that sole can be written as only)
'merely' is the second definition.
(I know that merely can be written as only)
(Other definitions for only that I've seen before include "And nothing more; sole" , "Unique; merely" , "And no one else" , "Existing alone with no other, perhaps a child" , "Alone; solitary" .)