Mountain peak cracked by ace climber? (4)
I believe the answer is:
bean
'climber?' is the definition.
(thesaurus)
'mountain peak cracked by ace' is the wordplay.
'mountain peak' becomes 'ben' (Scottish term for a peak as in Ben Nevis).
'cracked by' means one lot of letters goes inside another (to crack can mean to create a divide in).
'ace' becomes 'a' (**).
'ben' enclosing 'a' is 'BEAN'.
(Other definitions for bean that I've seen before include "Plant with seed in pod" , "Fava, kidney or mung, say" , "Haricot or runner?" , "Seed of a leguminous plant" , "Edible legume" .)