Heortology

Heortology is the word, however, is used to denote specifically the science of sacred festivals, embracing the principles of their origin, significance, and historical development, with reference to epochs or incidents in the Christian year.

From the 1913 Catholic Encyclopedia

Heortology (from the Greek ἑορτή, festival, and λογος, knowledge, discourse) etymologically implies a relation to feasts or festivals in general, an exposition of their meaning. The word, however, is used to denote specifically the science of sacred festivals, embracing the principles of their origin, significance, and historical development, with reference to epochs or incidents in the Christian year. (See Feasts, Ecclesiastical.)