Alpine goat (4)
I believe the answer is:
'alpine goat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ibex that I've seen before include "Mountain goat with curving horns" , "being nimble-footed" , "Mountain-goat" , "one seldom puts a foot wrong" , "Mountain goat with long curved horns" .)