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.
(..) Hey! On his heels! MAN: Take cover, man! Gillette, Mr.Sparrow has a dawn appointment with the gallows. I would hate for him to miss it. MAN: Search upstairs! MAN #: Look lively, men! (..)2003 Pirates of the Caribbean: The Curse of the Black Pearl