Make certain it is very complicated (9)
I believe the answer is:
intricate
'very complicated' is the definition.
(I've seen this before)
'make certain it' is the wordplay.
'make' indicates an anagram.
'certain'+'it'='certainit'
'certainit' is an anagram of 'INTRICATE'.
'is' is the link.
(Other definitions for intricate that I've seen before include "puzzling" , "Fancy" , "Complicated, detailed" , "puzzlingly obscure" , "Entangled" .)