Moderately attractive (6)
I believe the answer is:
pretty
This clue is a double definition.
'moderately' is the first definition.
(I know that moderately can be written as pretty)
'attractive' is the second definition.
(pretty can mean good-looking or attractive)
(Other definitions for pretty that I've seen before include "Fair - fairly" , "Facially attractive" , "Somewhat - attractive" , "Attractive - quite" , "Moderately" .)