dog days

noun[usually plural]3

1. •
   The unpleasantly hot days of late summer.

   • Why should those Etesian and Easterne winds blow cōtinually in some places, at set times, one way still, in the dog dayes only: heere perpetuall drought, there dropping showres; [...] — 1624
2. •
   Any similar period of inactivity, laziness, or stagnation.

   • The two-cassette miniseries, produced by Oliver Stone, arrives in early August, in time to stir the dog days of summer rentals. — 1993
3. •
   (no longer used) The days following the heliacal rising of Sirius, now in early August (Gregorian) at dates varying by latitude.

   • ... a sterre, wherof canicular or dogge days be named Dies caniculares. — 1538