noun

1. An act of becoming visible; appearance; visibility.

2. The thing appearing; a visible object; a form.

3. An unexpected, wonderful, or preternatural appearance; especially something such as a ghost or phantom.

   "The attic is haunted by the ghostly apparition of a young girl who died there."

4. The first appearance of a star or other luminary after having been invisible or obscured; opposed to occultation.

5. A period of consecutive days or nights when a particular celestial body may be observed, beginning with the heliacal rising of the body and ending with its heliacal setting.