HorologiumPronunciation: /ˌhɒrəˈləʊdʒɪəm, -ˈlɒdʒ-/ AstronomyDefinition of Horologium a faint southern constellation (the Clock), between Hydrus and Eridanus. Origin:LatinHorologium in other Oxford dictionaries Definition of Horologium in the US English dictionary