Of high mountains (6)
I believe the answer is:
alpine
'of high mountains' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for alpine that I've seen before include "Nepali (anag.)" , "Plant of high mountains" , "Relating to a European mountain range" , "from Germany, Austria etc" , "Native growing up in mountainous area" .)