Relentless ascent’s in confusion (9)
I believe the answer is:
incessant
'relentless' is the definition.
(thesaurus)
'ascent's in confusion' is the wordplay.
'confusion' is an anagram indicator.
'ascents'+'in'='ascentsin'
'ascentsin' with letters rearranged gives 'INCESSANT'.
(Other definitions for incessant that I've seen before include "Since Stan was continual." , "Unending" , "without a break" , "Perpetual, unremitting" , "Constant, unremitting" .)