Active set can climb (6)
I believe the answer is:
ascent
'climb' is the definition.
(I know that climb can be written as ascent)
'active set can' is the wordplay.
'active' indicates an anagram (the letters are active/moving).
'set'+'can'='setcan'
'setcan' with letters rearranged gives 'ASCENT'.
(Other definitions for ascent that I've seen before include "Enacts in climb" , "A climb or way up" , "The climbing of a peak" , "Uphill journey" , "Mountain path" .)