The expression "dog days of summer" appears to derive from ancient Greek and Roman mythology according to which the star Sirius was indicative and probably responsible for the hottest days in summer:

  • The ancient Greeks noticed that summer’s most intense heat occurred during the approximate 40-day period in the early summer when Sirius, the brightest star in the sky, rose and set with the sun. To them it was simple math. The daytime addition of the warmth of Sirius—ancient Greek for “glowing” or “scorcher”—to the blaze of the sun equaled extreme heat. According to Greek mythology, Sirius was the dog of the hunter Orion, and the ancient Romans placed the star in the constellation Canis Major (Latin for “Greater Dog”). The Romans thus referred to the sweltering period when the rising of the sun and Sirius converged as the “dies caniculares” or “days of the dog star.” (www.history.com)

The expression entered the English language in the 16th century:

  • 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). (etymonline).

The same expression remained similar to the Latin "caniculares" in other languages such as canicula in Portuguese, canicula in Spanish, canicola in Italian and canicule in French where the term has an older, medieval usage.

  • Was the term "canicola" used before "dog days" entered English common usage or was the expression unknown before the 16th century.

  • Was the expression imported or translated at that time by some some 16th century English writer?

  • 1
    It might help to note that the first citation in the full OED for dog day is 1538 T. Elyot Dict. Canicula..a sterre, wherof canicular or dogge days be named Dies caniculares. Aug 23, 2016 at 15:49
  • Perhaps related to another mystery - where the word dog came from.
    – Phil Sweet
    Aug 24, 2016 at 4:58

1 Answer 1


An earlier term was canicular days, variously spelled. This term still surfaces from time to time, although mostly as a novelty (as in this 2011 Space.com article) or as the peculiar choice of some or other translation dictionary (as in the title of this 2015 acupuncture paper, 三伏天 being rendered in some citations as dog days or dog days of summer).

The OED has it from Latin, akin to the French caniculaire, from 1398 in John Trevisa's translation of the friar Bartholomew de Glanville's De Proprietatibus Rerum:

In the mydle of the monthe Iulius the Canicular dayes begyn.

The next is from Richard Arnold's Chronicle, ca. 1503:

The Canycular daies begynne ye xv kalendas of august and endure to the iiij. nonas of septembre.

There is an explanatory note on the differing dates:

The dog days have been variously reckoned, as depending on either the Greater Dog Star (Sirius) or the Lesser Dog Star (Procyon), and on either the heliacal rising or the cosmical rising (which occurs at an earlier date). The timing of these risings depends on latitude, and they do not occur at all in most of southern hemisphere; in addition, owing to the precession of the equinox they now take place later in the year. As a result very different dates have been assigned for the dog days, their beginning ranging from 3 July to 15 August, and their duration varying from 30 to 61 days. In the Calendar of the 1552 Book of Common Prayer they run from 7 July to 5 September. In current calendars they are often said to begin on 3 July and end on 11 August (i.e. the 40 days preceding the cosmical rising of Sirius at the latitude of Greenwich).

The earliest entry for dog days appears in Thomas Elyot's 1538 dictionary as

Canicula..a sterre, wherof canicular or dogge days be named Dies caniculares.

The shorter, alliterative variant no doubt supplanted the Latinate word over time, though it is difficult to ascertain when using online tools.

  • 3
    What an odd coincidence that the dog days of summer are called 三伏天 in Chinese. The Chinese name literally means ‘the three crouching/subdued/lying-low days’; but the character 伏 ‘lie low/crouch down’ is actually made up of 亻 (= 人) rén ‘person’ and 犬 quǎn ‘dog’, representing a dog lying crouched next to its master in submission. Aug 23, 2016 at 16:39
  • Nice answer. So if the earliest usage is a dictionary entry, the expression "dog days" must have been used before to some extent. It might have been introduced as a more English, colloquial expression compared to the Latin one, but I doubt it was coined by ordinary people.
    – user66974
    Aug 23, 2016 at 17:04

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