Smooth covering for walls and ceilings (7)
I believe the answer is:
plaster
'smooth covering for walls and ceilings' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for plaster that I've seen before include "Smear" , "Adhesive dressing" , "First-aid item" , "Stuff that sticks on ceilings or wounds" , "Adhesive material" .)