Dog Days Definition

Origin of Dog Days

• Attested in English since 1538, from Latin dies caniculares, translated from Ancient Greek; originally a reference to the hot summer days (in the Northern Hemisphere) when Sirius (the Dog Star), in Canis Major, rose and set with the Sun (heliacal rising). The Greeks also made reference to these "dog days", and for the ancient Egyptians, circa 3000 BCE, the rising of this star coincided with the summer solstice and the start of Nile flooding. The "dog" association apparently began here, as the star's hieroglyph was a dog, a watchdog for the flooding of the Nile.

  From Wiktionary

• Translation of Late Latin diēs canīculārēs Dog Star days (so called because the Dog Star (Sirius) rises and sets with the sun during this time) Latin diēs pl. of diēs day Late Latin canīculārēs pl. of canīculāris of the Dog Star

  From American Heritage Dictionary of the English Language, 5th Edition