Uncontrollable zest in calling a philosopher (9)
I believe the answer is:
nietzsche
'a philosopher' is the definition.
(I've seen this before)
'uncontrollable zest in calling' is the wordplay.
'uncontrollable' is an anagram indicator (I've seen this in other clues).
'in' indicates putting letters inside.
'calling' becomes 'niche' (I've seen this before).
'zest' is an anagram of 'etzs'.
'etzs' inserted inside 'niche' is 'NIETZSCHE'.
(Other definitions for nietzsche that I've seen before include "19th century German philosopher who divided mankind into master class and herd" , "Friedrich -, nineteenth century German philosopher" , "German philosopher, wrote Beyond Good and Evil" , "Influential German existentialist philosopher" , "German poet" .)