Definitely not in duplicate (3,3,3)
I believe the answer is:
out and out
'definitely' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for out and out that I've seen before include "verdicts leading up to hat-trick ball" , "Total" , "In every respect" , "flat" , "Absolute; completely" .)