the study of the history and significance of the feasts and seasons in the ecclesiastical calendar.
Origin of heortology
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
"study of religious feasts and calendars," 1900, from Greek heorte "feast" + -ology. The immediate source of the English word is in French or German.
Online Etymology Dictionary, © 2010 Douglas Harper