The story
From the fact that the star lies in the constellation of Canis Major (the "larger dog").
Etymology from Wiktionary, CC BY-SA 4.0.
Dog Star
Today it means: A bluish-white star in the constellation Canis Major; Alpha (α) Canis Majoris A. A vertex of the Winter Triangle and the brightest star in the night sky. It is actually a binary star with a white dwarf companion star. Full definition →