Unassisted (6-6)
'unassisted' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for single-handed that I've seen before include "Without assistance" , "Glen dashed in (anag) -- entirely alone" , "Unaided" , "Working alone" , "Done without help from others" .)
'unassisted' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for unaided that I've seen before include "Without help or support" , "Without extra help" , "Done by oneself alone" , "Quite without assistance" , "Without help or assistance" .)