dog days definition by American Heritage Dictionary
The hot, sultry period of summer between early July and early September.
A period of stagnation.
Origin: 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.
Hot, sultry summer weather; also, a period of stagnation. For example, It's hard to get much work done during the dog days, or Every winter there's a week or two of dog days when sales drop dramatically. The term alludes to the period between early July and early September, when Sirius, the so-called Dog Star, rises and sets with the sun. The ancient Romans called this phenomenon dies caniculares, which was translated as “dog days” in the first half of the 1500s.