Mountaineer's goal (4)
I believe the answer is:
acme
'mountaineer's goal' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acme that I've seen before include "Height of perfection" , "Aim of mountaineers" , "High point of excellence" , "Zenith - optimum" , "Summit - climax" .)