It is said negative answer resembles whinny (5)
I believe the answer is:
neigh
'whinny' is the definition.
(I know that whinny can be written as neigh)
'it is said negative answer' is the wordplay.
'it is said' indicates a 'sounds like' (homophone) clue.
'negative answer' becomes 'nay' (archaic form of 'no').
'nay' sounds like 'NEIGH'.
'resembles' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for neigh that I've seen before include "Horse's noise" , "Comment from stallion" , "Hinge (anag.)" , "Horse's whinny" , "Comment from Arab" .)