Intrepid beating Mount Everest endlessly (11)
I believe the answer is:
venturesome
'intrepid' is the definition.
(thesaurus)
'beating mount everest endlessly' is the wordplay.
'beating' indicates anagramming the letters.
'endlessly' means to remove the last letter.
'mount'+'everest'='mounteverest'
'mounteverest' with its last letter taken off is 'mounteveres'.
'mounteveres' is an anagram of 'VENTURESOME'.
(Other definitions for venturesome that I've seen before include "Prepared to take risks" , "Bold" , "Willing to take risks" .)