It’s laid down (3)

I believe the answer is:

law

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'down' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

I don't understand the rest of the clue.

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(Other definitions for law that I've seen before include "Regulation" , "Rule of conduct" , "Act" , "'Possession is nine points of the ...'" , "Edict" .)

I've seen this clue in the Evening Standard.

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