Retro style (4)
I believe the answer is:
deco
'retro style' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for deco that I've seen before include "Art's partner" , "Style of design popular in the 1920s and 1930s" , "Art -, C 20 style of ornamentation" .)