Section of a legal document (6)
I believe the answer is:
clause
'section of a legal document' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for clause that I've seen before include "Joker, eg" , "Subunit of a sentence" , "More than a phrase and not quite a sentence" , "part of legal document" , "Section in a contract" .)