Acme (4)
'acme' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for zenith that I've seen before include "The highest point directly above" , "Top point" , "The acme" , "Greatest height" , "Peak" .)
'acme' is the definition.
(synonyms)
This is all the clue.
(Other definitions for apex that I've seen before include "high-point" , "Top point" , "Topmost point" , "Top, highest part" , "Summit - pinnacle" .)