Mountaineer out for the count (11)
I believe the answer is:
enumeration
'the count' is the definition.
('enumeration' can be a synonym of 'count')
'mountaineer out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'mountaineer' anagrammed gives 'ENUMERATION'.
'for' is the link.
(Other definitions for enumeration that I've seen before include "Act of counting" , "Counting process" , "The act of numbering" , "The act of mentioning one by one" .)