Dog day

from The Collaborative International Dictionary of English v.0.48

Dog day \Dog" day`\ or Dogday \Dog"day`\
   One of the dog days.
   [1913 Webster]

   {Dogday cicada} (Zool.), a large American cicada ({Cicada
      pruinosa}), which trills loudly in midsummer.
      [1913 Webster] Dog days