Crossword Genius

Not the whole area (3)

Ross

I believe the answer is:

are

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

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for are that I've seen before include "is for more than one" , "(We/you/they) exist" , "live" , "Unit of land measure equal to 100 square metres" , "Exist; square measure" .)

I've seen this clue in the Evening Standard.
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