Plain, bare (9)
I believe the answer is:
unadorned
I believe this is a double definition.
'plain' is the first definition.
(associated in meaning)
'bare' is the second definition.
(thesaurus)
(Other definitions for unadorned that I've seen before include "Without embellishment" , "Plain, undecorated" , "Simple and plain as around den" , "Not decorated, plain and simple" .)