Son set my new method (6)
I believe the answer is:
system
'method' is the definition.
(I know that system is a type of method)
'son set my new' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'new' is an anagram indicator.
'set'+'my'='setmy'
'setmy' with letters rearranged gives 'ystem'.
's'+'ystem'='SYSTEM'
(Other definitions for system that I've seen before include "coherent plan" , "Organised scheme" , "A complete methodology" , "Method, set of connected things" , "A complete set of procedures for doing something" .)