Set form of words or method (7)
I believe the answer is:
formula
'set form of words or method' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for formula that I've seen before include "Category in motor racing" , "Mathematical expression for solving problems" , "Set form of words or mehod" , "Modus operandi" , "Mathematical rule expressed in algebraic symbols" .)