"study of religious feasts and calendars," 1881, from Greek heorte "a feast or festival, holiday," + -ology. The immediate source of the English word is in French or German. Related: Heortological (1880).
Entries linking to heortology
-ology
word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.
The second element is prop[erly] -logy (-logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary]