Formal account of a matter (6)
I believe the answer is:
report
'formal account of a matter' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for report that I've seen before include "Formal account of a matter" , "Formal document" , "Spoken/written account" , "Complain about; noise" , "Make a complaint about (someone)" .)