As a rule, is it spoken? (9,3)
I believe the answer is:
unwritten law
'as a rule is it' is the definition.
I can't judge whether this definition defines the answer.
'spoken?' is the wordplay.
I cannot quite see how this works, but
'spoken?' could be 'unwritten' ('unwritten' can be similar in meaning to 'spoken') and 'unwritten' is found in the answer.
The remaining letters 'law' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for unwritten law that I've seen is " Accepted rule".)