A portico in Greek architecture (4)
I believe the answer is:
stoa
'a portico in greek architecture' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stoa that I've seen before include "Philosophers' porch" , "old school" , "Portico or roofed colonnade" , "Greek portico or colonnade" , "Venue for Greek philosophers" .)