Ring-shaped; forming a ring (7)
I believe the answer is:
annular
I believe this is a double definition.
'ring-shaped' is the first definition.
(synonyms)
'forming a ring' is the second definition.
(I've seen this before)
(Other definitions for annular that I've seen before include "in a band" , "Shaped like a ring" , "Circular" , "Ring-shaped" , "Doughnut-shaped -- a LAN run (anag)" .)