We are calling to 'confirm your appointment' with Dr. Jones. = We are calling to make sure that you will 'keep your appointment' with Dr. Jones.
The museum is open to visitors 'by appointment' only. [=you have to make an appointment to visit the museum]
The court ordered the 'appointment' of an attorney to represent the child.
(..) ELVIRA: You just missed Frank. TONY: Too bad. OnIy I didn't come to see Frank. ELVIRA: This is not the time or the pIace, Tony. ELVIRA: Make an appointment. TONY: That's okay. I got something important I want to taIk to you about. -Sure. Why not? -Okay. I won't bite you. (..)1983 Scarface