Athenian garret (5)
I believe the answer is:
attic
I believe this is a double definition.
'athenian' is the first definition.
(I've seen this in another clue)
'garret' is the second definition.
(synonyms)
(Other definitions for attic that I've seen before include "Athenian - garret" , "Top level" , "Tacit (anag.)" , "room with lots of junk?" , "28 [GREEK]" .)