Prescribed by law (9)
I believe the answer is:
statutory
'prescribed by law' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for statutory that I've seen before include "Of written law as to a trusty" , "Legally prescribed" , "Try-outs at being required by law" , "Relating to written law" , "In accordance with written law" .)