Very extensive, like a carpet (4-2-4)
I believe the answer is:
wall-to-wall
'very' is the definition.
Both the definition and answer are adjectives.
Maybe you can see a link between them that I don't see?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for wall-to-wall that I've seen before include "Widespread" , "(Of carpet) fitted" .)