Doctor's client, long-suffering (7)
I believe the answer is:
patient
I believe this is a double definition.
'doctor's client' is the first definition.
(I've seen this before)
'long-suffering' is the second definition.
('patient' can be similar in meaning to 'long-suffering')
(Other definitions for patient that I've seen before include "doctor's client" , "Cool" , "Calm" , "Prepared to wait" , "One being treated" .)