Greek order of architecture (5)
I believe the answer is:
doric
'greek order of architecture' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for doric that I've seen before include "Type of column" , "Greek architectural style" , "Greek dialect" , "Plainest order of Gk. architecture" , "Of the oldest and simplest form of architecture" .)