What is the origin of horologium?
There are nearly a score—20!—spellings in Middle English for horologium, and nearly as many in Old French. Horologium comes from the Latin noun hōrologium “an instrument for showing the time, a dial, sundial, hourglass, clock, clepsydra (water clock).” Hōrologium is a Latin borrowing of Greek hōrológion with the same meaning. Greek hōrológion is a compound of hōrológos “teller of time” and the diminutive noun suffix -ion. Hōrológos is a compound of hṓra “year, season, hour, time, time of day, the right time, time of ripening or florescence,” which was taken into Latin wholesale as hōra with all its meanings (hour comes into English via Old French from Latin). The element or word logos “word, speech, account, computation, reason” is very familiar in English as the suffix –logy, as in philology, theology, paleontology. Horologium entered English in the second half of the 14th century.