: a small book or calendar in which one writes planned or scheduled dates, appointments, etc.
Open my datebook to any day of the week and it's the same story: My daughter is running in a cross-country meet and my younger son is playing baseball. Joyce Maynard
also: a place on a computer or other device for entering similar information
… pull out your calendars or your digital datebook and mark Aug. 20 on your calendar because the MuckFest 5k is coming to town. Rachel Wittrock