Stated number in addition (3)
I believe the answer is:
too
'in addition' is the definition.
(thesaurus)
'stated number' is the wordplay.
'stated' shows a homophone (sound like).
'number' becomes 'two' (two is a kind of number).
'two' sounds like 'TOO'.
(Other definitions for too that I've seen before include "Unduly" , "What a pity!" , "As well, also" , "Likewise" , "On top - also" .)