Acknowledgement from District Attorney about assignment (9)
I believe the answer is:
admission
'acknowledgement' is the definition.
(admission is a kind of acknowledgement)
'district attorney about assignment' is the wordplay.
'district attorney' becomes 'DA' (abbreviation).
'about' is a reversal indicator.
'assignment' becomes 'mission' (mission is a kind of assignment).
'da' reversed gives 'ad'.
'ad'+'mission'='ADMISSION'
'from' is the link.
(Other definitions for admission that I've seen before include "A confessing" , "for which one may be charged" , "Anything conceded" , "Access" , "cost of entry?" .)