Late 16th century; earliest use found in Thomas Blundeville (fl. 1561), author and translator. From south + triangle, after post-classical Latin Triangulum australe.
Definition of South Triangle in US English:
South Triangle
noun
Astronomy rare, historical
= Southern Triangle.
Origin
Late 16th century; earliest use found in Thomas Blundeville (fl. 1561), author and translator. From south + triangle, after post-classical Latin Triangulum australe.