Solely (4)
'solely' is the definition.
(I know that solely can be written as only)
This is all the clue.
(Other definitions for only that I've seen before include "Merely; single" , "Solely, lone" , "And nothing more; sole" , "Simply" , ". . . . the Lonely (sung by Roy Orbison)" .)
'solely' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for merely that I've seen before include "'Only, and nothing more (6)'" , "Just one" , "Simply - only" .)