Island or large isle at sea (5)

I believe the answer is:

ellis

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'island or' is the definition.
I can't tell whether this definition defines the answer.

'large isle at sea' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'at sea' indicates anagramming the letters.
'l'+'isle'='lisle'
'lisle' with letters rearranged gives 'ELLIS'.

Can you help me to learn more?

(Other definitions for ellis that I've seen before include "Havelock --, psychologist" , "-- Island, New York entry point" , "- Peters, wrote Brother Cadfael books" , "Havelock --, English essayist" , "American island" .)

I've seen this clue in The Independent.

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