Have a drink during the climb, I believe (6)
I believe the answer is:
imbibe
'have a drink' is the definition.
(I've seen this in another clue)
'during the climb i believe' is the wordplay.
'during' says the answer is hidden in the clue.
'IMBIBE' is hidden in the letters of 'climb i believe'.
(Other definitions for imbibe that I've seen before include "Drink or absorb into mind" , "Take in (with one's mother's milk?)" , "Swallow" , "Partake of drink" , "Quaff" .)