Nick is excellent with top (5)
I believe the answer is:
notch
I believe this is a double definition.
'nick' is the first definition.
(synonyms)
'excellent with top' is the second definition.
('top notch' means excellent)
'is' acts as a link.
(Other definitions for notch that I've seen before include "Gouge" , "Incision on an edge" , "Cleft" , "Mark indented in wood etc" , "Nick - score" .)