Tibetans call it Chomolungma (7)
I believe the answer is:
everest
'tibetans call it chomolungma' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for everest that I've seen before include "Tee revs up the mountain" , "Himalyan peak" , "Great achievement" , "The highest mountain of all (7)" , "High mountain" .)