Affirmative reply (3)
(Other definitions for exactly that I've seen before include "Precisely thus" , "In precise terms" , "Indeed; verbatim" , "Dead" , "Quite so" .)
'affirmative reply' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for yes that I've seen before include "3 across" , "Confirmation" , "Validating vote" , "Of course" , "Indeed" .)
(Other definitions for yea that I've seen before include "Affirmative vote" , "Emphatic agreement" , "Approval" , "Affirmative in the British Parliament" , "Positive vote" .)
(Other definitions for aye that I've seen before include "Always" , "Indeed" , "Yes vote" , "Word of assent" , "Yes, at the double for the sailor" .)