Left grates out of greatest dimensions (7)

I believe the answer is:

largest

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'left grates out of greatest dimensions' is the definition.
I can't tell whether this defines the answer.

'left grates out of' is the wordplay.
'left' becomes 'l' (common abbreviation).
'out of' is an anagram indicator.
'grates' anagrammed gives 'argest'.
'l'+'argest'='LARGEST'

Can you help me to learn more?

(Other definitions for largest that I've seen before include "Most ample" , "Biggest" , "Extremely generous" , "Maximum" , "Chief" .)

I've seen this clue in The Daily Express.

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