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dog days (n.)[dog days 词源字典]: 1530s, from Latin dies caniculares, from Greek; so called because they occur around the time of the heliacal rising of Sirius, the Dog Star (kyon seirios). Noted as the hottest and most unwholesome time of the year; usually July 3 to Aug. 11, but variously calculated, depending on latitude and on whether the greater Dog-star (Sirius) or the lesser one (Procyon) is reckoned.

The heliacal rising of Sirius has shifted down the calendar with the precession of the equinoxes; in ancient Egypt c. 3000 B.C.E. it coincided with the summer solstice, which also was the new year and the beginning of the inundation of the Nile. The "dog" association apparently began here (the star's hieroglyph was a dog), but the reasons for it are obscure.[dog days etymology, dog days origin, 英语词源]
ember-days (n.): Old English Ymbrendaeg, Ymbren, 12 days of the year (divided into four seasonal periods, hence Medieval Latin name quatuor tempora) set aside by the Church for fasting and prayers, from Old English ymbren "recurring," corruption of ymbryne "a circuit, revolution, course, anniversary," literally "a running around," from ymb "round" (cognate with Greek amphi, Latin ambo; see ambi-) + ryne "course, running" (see run (n.)). Perhaps influenced by a corruption of the Latin name (compare German quatember, Danish tamper-dage). The Wednesday, Friday, and Saturday after the first Sunday in Lent, Whit-Sunday, Sept. 14, and Dec. 13, set aside for prayer and fasting.
nowadays (adv.): late 14c., contracted from Middle English nou adayes (mid-14c.), from now + adayes "during the day," with adverbial genitive (see day).