Interoffice message (4)
I believe the answer is:
memo
'interoffice message' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for memo that I've seen before include "It will remind" , "Note written as a reminder" , "- Currie, Br. politician" , "Reminder (abbr)" , "Short note or message" .)