What made you laugh in the doctor's waiting room? (4,6)

'waiting room?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'what made you laugh in the doctor's' is the wordplay.
I cannot really understand how this works, but
'you' could be 'u' (homophones) and 'u' is found in the answer.
'doctor' could be 'mo' (medical officer) and 'mo' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?