Note: An apartment (1,4)

I believe the answer is:

a flat

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'note' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'an apartment' is the wordplay.
'an' becomes 'a'.
'apartment' becomes 'flat' (synonyms).
'a'+'flat'='A FLAT'

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I've seen this clue in The Hindu.

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