"Definitely!" (3,4)
'definitely' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for without fail that I've seen before include "Definitely" , "Always" , "For certain" , "for sure" , "Like dumbed-down exam results" .)
'definitely' is the definition.
('definitely' can be used to say 'yes')
This is the entire clue.
(Other definitions for yes that I've seen before include "OK" , "Confirmation" , "Oui" , "Word of affirmation" , "Pro vote" .)
'definitely' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for for sure that I've seen before include "Indeed" , "Of a certainty" .)