Definitely not included in declaration of earnings (2,4)
I believe the answer is:
no fear
'definitely not' is the definition.
(I've seen this before)
'included in declaration of earnings' is the wordplay.
'included in' indicates a hidden word.
'NO FEAR' is hidden in the letters of 'declaration of earnings'.
(Other definitions for no fear that I've seen before include "What 7 [INTREPID] person will have" , "Absolutely not" , "Not on your life, certainly not" , "Definitely not (informal)" , "What brave man displays" .)