Mountain goat (4)
I believe the answer is:
'mountain goat' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ibex that I've seen before include "Wild mountain goat" , "Large-horned mountain goat" , "Mountain-goat" , "Wild goat with double curved horns" , "Wild goat with large recurved horns" .)