Timetable (8)
(Other definitions for calendar that I've seen before include "Schedule" , "Tabular array of days" , "Chart showing seasons etc" , "System for dividing the year" , "Diary" .)
'timetable' is the definition.
(I know that timetable can be written as schedule)
This is the entire clue.
(Other definitions for schedule that I've seen before include "List of duties, etc" , "List of intended events and times" , "Clues he'd dropped about timetable" , "Syllabus" , "Plan for an activity" .)