Crux Syllabification: (Crux)Pronunciation: /krəks, kro͝oks/ AstronomyDefinition of Crux another term for the Southern Cross. (as genitive Crucis /ˈkro͞osis/) used with a preceding letter or numeral to designate a star in this constellation:the star Beta CrucisOrigin:LatinCrux in other Oxford dictionaries Definition of Crux in the British & World English dictionary