Design unfinished and home undecorated (5)
I believe the answer is:
plain
'undecorated' is the definition.
(associated in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for plain that I've seen before include "Unadorned on flat area" , "lament" , "Uncomplicated" , "not striking" , "Simple, unadorned" .)