Stress concerning angry packing note (9)
I believe the answer is:
reiterate
'stress' is the definition.
(both can mean to emphasise)
'concerning angry packing note' is the wordplay.
I cannot quite understand how this works, but
'concerning' could be 're' (both can mean on a particular topic) and 're' is found in the answer.
'note' could be 'te' (musical note) and 'te' is found within the answer.
'angry' could be 'irate' (similar in meaning) and 'irate' is located in the leftover letters.
No letters remain.
This explanation may well be incorrect...
(Other definitions for reiterate that I've seen before include "Say it again for tire eater" , "Restate" , "Recapitulate" , "Repeat" , "Say something a number of times" .)