Crossword Genius

A large container of herrings (8)

Ross

I believe the answer is:

atlantic

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

'container of herrings' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

'a large' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
'large' could be 'l' (eg in clothes sizes) and 'l' is present in the answer.
The remaining letters 'attic' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for atlantic that I've seen before include "Latin cat strangely in the sea" , "Sea between Old and New Worlds" , "Azores, Falklands, in it" , "main" , "New Jersey resort" .)

I've seen this clue in the Evening Standard.
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