Branch from ascent leaving summit (4)
I believe the answer is:
limb
'branch' is the definition.
(I know that branch can be written as limb)
'ascent leaving summit' is the wordplay.
'ascent' becomes 'climb' (synonyms).
'leaving summit' means to remove the first letter (the top or summit of the word is removed).
'climb' with its first letter taken away is 'LIMB'.
'from' is the link.
(Other definitions for limb that I've seen before include "Eg wing" , "Substantial branch from a tree trunk" , "Part of body or branch of tree" , "Bough" , "A supporter" .)