Endless criticism involving old philosopher (5)
I believe the answer is:
stoic
'philosopher' is the definition.
(type of ancient philosopher)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stoic that I've seen before include "he's not complaining" , "Impassive type" , "Unemotional" , "Athenian philosopher" , "One patient under misfortune" .)