Horologion

The horologion or horologium (pl. horologia), also known by other names, is the book of hours for the Eastern Orthodox and Eastern Catholic Churches. It provides the acolouthia (, akolouthíai), the fixed portions of the Divine Service used every day at certain canonical hours. Additional parts of the service are changed daily, mostly according to the Menologium.

==Names== is the latinized version of the Greek hōrológion (), from hṓra (, "time period, hour"), lógos (, "writing, recording") + -ion (), together originally meaning a sundial, clepsydra, or other timekeeping device. (The same roots are used in horology, the scientific study of time.) In Byzantine Greek, the word was repurposed to also denote the Eastern books of hours, records of the hymns and prayers to be offered at the proper times of each day. The plural form of both the Latin and Greek forms of the word is horologia.