In addition comes to nothing (3)
I believe the answer is:
too
'in addition' is the definition.
(I've seen this before)
'to nothing' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'to'+'o'='TOO'
'comes' acts as a link.
(Other definitions for too that I've seen before include "Moreover, in addition" , "What a pity!" , "To a greater than desirable extent" , "As well, also" , "Unduly" .)