Drink needed after Foreign Office meeting (5)
I believe the answer is:
Here is my best explanation:
'meeting' is the definition.
(forum is a kind of meeting)
'drink needed after foreign office' is the subsidiary indication.
'drink' becomes 'rum' (rum is a kind of drink).
'needed after' is a charade indicator (letters next to each other).
'foreign office' becomes 'fo'.
'rum' put after 'fo' is 'forum'.
(Other definitions for forum that I've seen before include "Roman meeting place", "Meeting-place", "Medium for discussion", "Arena for debate", "place for debate", "Ancient Roman marketplace or place for public discussions", "Marketplace", "Place of assembly for the people in ancient Greece", "Public meeting or assembly for open discussion" and "Discussion meeting".)