Sort of answer seemingly long unused (5)
I believe the answer is:
dusty
'unused' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I don't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for dusty that I've seen before include "Mr Miller" , "Miller - or answer, may be!" , "Old-fashioned" , "Covered in fine powder" , "In need of a spring clean" .)