Southern Cross vs Crux

Southern Cross and Crux both are nouns.

Word	Noun	Adjective	Verb	Adverb
Southern Cross	Yes	No	No	No
Crux	Yes	No	No	No

As nouns, Southern Cross and Crux are synonyms defined as:

Southern Cross and Crux: a small conspicuous constellation in the Southern Hemisphere in the Milky Way near Centaurus

Other synonyms of Southern Cross include Crux Australis.

Southern Cross (noun)	Crux (noun)
a small conspicuous constellation in the Southern Hemisphere in the Milky Way near Centaurus	a small conspicuous constellation in the Southern Hemisphere in the Milky Way near Centaurus