CaelumPronunciation: /ˈsiːləm/ AstronomyDefinition of Caelum a small and faint southern constellation (the Chisel), next to Eridanus. (as genitive Caeli /ˈsiːli/) used with preceding letter or numeral to designate a star in this constellation:the star Beta CaeliOrigin:LatinCaelum in other Oxford dictionaries Definition of Caelum in the US English dictionary