Communist in orderly retreat (3)
I believe the answer is:
red
'communist' is the definition.
(red can informally mean communist)
'in orderly retreat' is the wordplay.
'in' says the answer is hidden in the clue.
'retreat' says the letters should be written backwards.
'der' is hidden within 'orderly'.
'der' reversed gives 'RED'.
(Other definitions for red that I've seen before include "Warning light colour" , "Colour of communism" , "- Cross; - carpet" , "The colour of the former Russian army" , "Glowing" .)