All in a Day's Work
Our word day had its immediate ancestor in the Old English daeg. I must admit that I was surprised when the Oxford English Dictionary told me that it is “in no way related to the Latin dies”; I would have thought it was. Instead, its predecessors (Aryan, Sanskrit, Lithuanian) carried the meaning "the hot or burning time."
We still retain the word now-a-days, also rendered as here-a-days centuries ago, and it is fitting that it was once balanced by then-a-days.
Evidently, in the day, there were many days dedicated to certain customs, events, or duties, and many phrases containing -days as a combining form were thus formed. With no particular rhyme or reason, here are some of them, all culled from the OED.
• bind days: days on which tenants were bound to render stated unpaid service to their feudal lord; boon-days.
• chair-days: old age, when rest in a chair is the most natural condition.
• daft days: the days of merriment at Christmas.
• darg-days: days of work done in lieu of rent or due to the feudal lord. [syncopated form of daywork]
• dog-days: the days about the time of the heliacal rising of the Dog-star; noted from ancient times as the hottest and most unwholesome period of the year.
• Egyptian days: the two days in each month which were believed to be unlucky.
• fern-days, days of old. [ON forn, ancient]
• fuir-days: Late in the day. [far days, forth days]
• gang-days: the three days preceding Ascension-day or Holy Thursday; also called Rogation-days. [so called from the processions held on these days; gang = way or passage.]
• Indicant Days: among Physicians, those Days which signify that a crisis or change in a disease will happen on such a day.
• Nestor's days: old age, long life. [wise old king mentioned in the Iliad]
• riding days: the days of Border raiding. [Scotland]
• roaring days (Austral.): the time of the Australian gold-rush.
• Robin Hood's days: festival time, when a mummer’s play would present the story of Robin Hood.
• salad days: days of youthful inexperience.
• ship's days: the days allowed for loading and unloading a ship.
• the last days: the period including and immediately preceding the Last Judgement.
SIDEBAR: this day in history
(substitute @ for AT above)