Crossword Genius

It could be written grammatically (4,10)

Ross

I believe the answer is:

past participle

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'it could be written grammatically' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

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(Another definition for past participle that I've seen is " had, say".)

I've seen this clue in The Sunday Times and The Times.
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