Mountaineer scrambling list (11)
I believe the answer is:
enumeration
'list' is the definition.
(enumeration is a kind of list)
'mountaineer scrambling' is the wordplay.
'scrambling' indicates anagramming the letters.
'mountaineer' with letters rearranged gives 'ENUMERATION'.
(Other definitions for enumeration that I've seen before include "Counting process" , "The act of mentioning one by one" , "Act of counting" , "The act of numbering" .)