A lot of criticism about old patient (5)
I believe the answer is:
stoic
'patient' is the definition.
(stoic can mean patient or tolerating suffering)
I cannot 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 "Greek philosopher" , "Seeming unaffected by pleasure or pain" , "Unflappable type" , "he's not complaining" , "not given to complaining" .)