Complex whole (6)
I believe the answer is:
system
'complex whole' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for system that I've seen before include "Organised structure for arranging or classifying" , "Organised method" , "My sets (anag.)" , "Set of things in a connected whole" , "Body of doctrine - method of procedure" .)