Order from Greek physician involving king and emperor (5)
I believe the answer is:
doric
'order from greek' is the definition.
(as in the Doric order of architecture)
'physician involving king and emperor' is the wordplay.
'physician' becomes 'doc' (synonyms).
'involving' means one lot of letters goes inside another.
'king and emperor' becomes 'RI' (Rex Imperator, imperial term for king and emperor).
'doc' going around 'ri' is 'DORIC'.
(Other definitions for doric that I've seen before include "Relating to a classical order of architecture" , "Greek architectural order" , "Classical building style" , "In a classical Greek style of architecture" , "Denoting a classic Greek style" .)