Definition of Canis Major
a small constellation (the Great Dog), said to represent one of the dogs following Orion. It is just south of the celestial equator and contains the brightest star, Sirius.
(as genitive Canis Majoris
/məˈdʒɔːrɪs/) used with preceding letter or numeral to designate a star in this constellation:the star Eta Canis Majoris