Yielding to top mountaineer (6)
I believe the answer is:
limber
'yielding' is the definition.
(thesaurus)
'top mountaineer' is the wordplay.
'top' means to remove the first letter.
'mountaineer' becomes 'climber' (I've seen this before).
'climber' with its initial letter removed is 'LIMBER'.
'to' is the link.
(Other definitions for limber that I've seen before include "Supple; flexible" , "Lithe" , "Agile and flexible" , "easily bent" , "Artillery equipment" .)