Just for show (4)
I believe this is a double definition.
'just' is the first definition.
(just can mean fair in the sense of showing justice)
'for show' is the second definition.
(fair is a kind of show)
(Other definitions for fair that I've seen before include "entertainment provided here" , "Reasonable target?" , "clean" , "Just right" , "Just; beautiful; blond" .)
'just for show' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ornamental that I've seen before include "Plant grown for attractive appearance" , "Decorative" , "non-functional" , "showy" , "Fancy" .)