Neither gets the number right (3)
I believe the answer is:
nor
'neither' is the definition.
(eg in the phrase 'neither do I')
'the number right' is the wordplay.
'the number' becomes 'no' (abbreviation).
'right' becomes 'r' (common abbreviation).
'no'+'r'='NOR'
'gets' is the link.
(Other definitions for nor that I've seen before include "It's also not" , "Neither one ... the other" , "And not; Norman (abbr.)" , "Conjunction meaning 'and not'" , "And not either" .)