Five years spent addressing packages (6)
I believe the answer is:
pentad
'five years' is the definition.
(I've seen this before)
'spent addressing packages' is the wordplay.
'packages' indicates the answer is hidden within the clue (the answer is 'packaged' within the clue).
'PENTAD' is hidden in the letters of 'spent addressing'.
(Other definitions for pentad that I've seen before include "small group" , "Half a decade" , "five years" , "quintet" , "Set of five things" .)