Ruse complicated for certain (4)
I believe the answer is:
sure
'certain' is the definition.
(I know that certain can be written as sure)
'ruse complicated' is the wordplay.
'complicated' indicates anagramming the letters (a complex or confusing ordering of the letters).
'ruse' with letters rearranged gives 'SURE'.
'for' acts as a link.
(Other definitions for sure that I've seen before include "Certain, confident" , "Definite" , "Completely confident that one is right" , "Completely certain" , "Agreed" .)