hora

Hora, horae is feminine, first declension, borrowed from Greek. The time it names is not ours. A Roman hour was one twelfth of the daylight, so it stretched in June and shrank in December, and only at the equinoxes did it run to sixty minutes. Hora sexta is therefore always noon and never six o'clock, which is worth remembering before you translate a battle's timings.

In the church corpus the horae are the canonical hours, the fixed points of the daily office, and a book of hours is a layman's version of it. Latin has no separate word for "o'clock": you say the number and let hora carry it. Italian ora, French heure, Spanish hora and English hour all descend from it.