What you must be if you want to see a busy doctor (7)
I believe the answer is:
patient
'doctor' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for patient that I've seen before include "Willing to wait" , "Sufferer" , "Long-suffering - one under treatment" , "Uncomplaining - tolerant" , "Cool" .)