Apex (6)

(Other definitions for acre that I've seen before include "region of ground" , "Four roods - Israeli port" , "Care about the land measure" , "Mediterranean port" , "Old unit of area - old port" .)

(Other definitions for acme that I've seen before include "Aim of mountaineers" , "Height of perfection" , "Top or highest point" , "'Highest point, apex (4)'" , "Summit, crowning point" .)

(Other definitions for peak that I've seen before include "Pointed mountain" , "Apex" , "Summit, often pointed" , "Tip" , "maximum pitch" .)

(Other definitions for cusp that I've seen before include "Point formed by two intersecting curves - point of transition" , "Horn of moon" , "Turning point on which important developments depend" , "Pointed end - division between signs of the zodiac" , "Prominence on a tooth" .)

(Other definitions for pinnacle that I've seen before include "Acme" , "tip-top" , "The highest point, summit" , "Height of success" , "Crown" .)

(Other definitions for high-water mark that I've seen before include "Tide line on the beach" , "How far tide comes up" .)

(Other definitions for summit that I've seen before include "High point" , "Top or extreme point" , "Crown" , "Pinnacle or crest" , "important meeting" .)

(Other definitions for top that I've seen before include "Toy; uppermost point" , "Most successful" , "The circus tent can be a big one" , "Zenith" , "Peak; child's toy" .)