Tacit arrangement in Room At The Top (5)
I believe the answer is:
attic
'room at the top' is the definition.
(room at the top of a house)
'tacit arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'tacit' with letters rearranged gives 'ATTIC'.
'in' is the link.
(Other definitions for attic that I've seen before include "Dusty room" , "Athenian Greek" , "Top level" , "where high-ups are found?" , "Of Athens" .)