It's rightly kept in Delaware (3)

I believe the answer is:

law

I'm a little stuck... Click here to teach me more about this clue!

'it's rightly' is the definition.
I can't tell whether this definition defines the answer.

'in delaware' is the wordplay.
'in' indicates a hidden word.
'LAW' can be found hidden inside 'delaware'.

'kept' is the link.

Can you help me to learn more?

(Other definitions for law that I've seen before include "Act" , "Regulation" , "Body of rules of conduct for a society" , "Rule prohibiting certain actions" , "Official rule" .)

I've seen this clue in the Evening Standard.

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