Bill in outhouse protected (6)
I believe the answer is:
shaded
'protected' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I don't see?
'bill in outhouse' is the wordplay.
'bill' becomes 'ad' (advertisement stuck on wall).
'in' means one lot of letters goes inside another.
'outhouse' becomes 'shed' (a shed is an outside building).
'ad' inserted inside 'shed' is 'SHADED'.
Can you help me to learn more?
(Other definitions for shaded that I've seen before include "Out of direct sunlight" , "Coloured in; screened from direct light" , "Sheltered" , "In comparative darkness" , "Crayoned in" .)