Group saving soldier on top of Everest alone (8)
I believe the answer is:
separate
'alone' is the definition.
(synonyms)
'group saving soldier on top of everest' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'saving' means one lot of letters goes inside another.
'soldier' becomes 'para' (short for paratrooper).
'on top of' suggests taking the first letters.
The first letter of 'everest' is 'e'.
'set' enclosing 'para' is 'separat'.
'separat'+'e'='SEPARATE'
(Other definitions for separate that I've seen before include "Different, distinct" , "Distinct; divide" , "Distinct or discrete" , "Divided -- distinct" , "Distinct, not joined" .)