A ring that's in the sea (5)
I believe the answer is:
atoll
'in the sea' is the definition.
I can't tell whether this defines the answer.
'a ring' is the wordplay.
'ring' becomes 'toll' (a bell tolls).
'a'+'toll'='ATOLL'
'that's' is the link.
Can you help me to learn more?
(Other definitions for atoll that I've seen before include "tropical island" , "Coral island with central lagoon" , "String of islands" , "Bikini, say" , "Coral island surrounding a lagoon" .)