Unquestionably (9)
'unquestionably' is the definition.
(I know that unquestionably can be written as decidedly)
This is the entire clue.
'unquestionably' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for doubtless that I've seen before include "Definitely not" , "Assuredly" , "Probably, certainly" , "Unquestionably" , "Positive" .)