The stars in the universe are sorted from small to large.

Canis major is a constellation, not a star. Just like you are familiar with Taurus and Sagittarius, there are 88 constellations in the whole sky. The 12 constellation you are familiar with is the zodiac. Canis major is not the place where the zodiac passes, so you won't often hear about it, but we know it.

Constellation is to group some stars that are easy to see by the naked eye according to their special positions and belong to the same constellation. By making a constellation system, it is convenient for us to point out the orientation of the stars in the sky. Just as we divide provinces, several big cities are like several main bright stars in the constellation, and the provincial boundaries are equivalent to the constellation boundaries.

There are many constellations whose main bright stars really look like the names of constellations, such as Leo, Cygnus, Orion, Sagittarius and so on.

So constellations and stars are not comparable at all, although there is only one word difference.