Nothing in code (6)
I believe the answer is:
cipher
This clue is a double definition.
'nothing' is the first definition.
(synonyms)
'code' is the second definition.
(I know that code can be written as cipher)
'in' acts as a link.
(Other definitions for cipher that I've seen before include "Symbol representing nought, thing of no importance" , "A message written in code" , "Code - 0" , "Key to a code" , "Person or thing of no importance, or the symbol 0" .)