Crossword Genius

A ring that's in the sea (5)

Ross

I believe the answer is:

atoll

I'm a little stuck... Click here to teach me more about this clue!

'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" .)

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