Crampon primarily used by supple mountaineer (7)
I believe the answer is:
climber
'mountaineer' is the definition.
(thesaurus)
'crampon primarily used by supple' is the wordplay.
'primarily' suggests taking the first letters.
'used by' is a charade indicator (letters next to each other).
'supple' becomes 'limber' ('limber' can be a synonym of 'supple').
The first letter of 'crampon' is 'c'.
'c'+'limber'='CLIMBER'
(Other definitions for climber that I've seen before include "Mountaineer" , "Plant such as ivy" , "Bonnington" , "Edward Whymper, for example" , "in the garden" .)