Son with pine twig (6)
I believe the answer is:
switch
'twig' is the definition.
(thesaurus)
'son with pine' is the wordplay.
'son' becomes 's'.
'with' becomes 'w' (abbreviation).
'pine' becomes 'itch' (to pine for and to itch for both mean to desire).
's'+'w'+'itch'='SWITCH'
(Other definitions for switch that I've seen before include "Change; false hair" , "Electrical control - change sides" , "Sudden quick change" , "Exchange; contactor" , "that turns on the power" .)