Taking part in climb, I begin to drink (6)
I believe the answer is:
imbibe
'to drink' is the definition.
(synonyms)
'taking part in climb i begin' is the wordplay.
'taking part in' says the answer is hidden in the clue.
'IMBIBE' can be found hidden inside 'climb i begin'.
(Other definitions for imbibe that I've seen before include "Swallow" , "Quaff" , "Take in (with one's mother's milk?)" , "Tope" , "Drink in - assimilate" .)