Athenian portico (4)
I believe the answer is:
stoa
'athenian portico' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stoa that I've seen before include "Roofed walkway with colonnades - oats (anag)" , "Venue for Greek philosophers" , "classical colonnade" , "A portico in Greek architecture" , "old school" .)