hebdomad
A group of seven.
obsolete
Let us now pass to the other species of the hebdomad, which is comprehended in the decad, and which exhibits an admirable nature no less than the former hebdomad. This, therefore, is composed of one, two, and four, which possess two most harmonic ratios, the duple and the quadruple; the former of which forms the symphony diapason, and the latter the symphony desdiapason.
A period of seven days; a week.
historical
For that ſaying of our Saviour, My Father worketh hitherto, and I work, is by the moſt judicious underſtood of the works of preſervation and providence: Thoſe of creation being concluded within the firſt Hebdomade, accordingly as is expreſt in the Hiſtory, that God on the ſeventh day reſted from all his works.
A group of seven world-creating archons (supernatural beings) often regarded as somewhat hostile; also, a term of address for the Demiurge (“a being sometimes seen as the creator of evil”).
When, then, the Great Archon had been orally instructed, and every creature of the Ogdoad had been orally instructed and taught, and [after] the mystery became known to the celestial [powers], it was also necessary that afterwards the Gospel should come to the Hebdomad, in order likewise that the Archon of the Hebdomad might be similarly instructed and indoctrinated into the Gospel.
Where it comes from
From Late Latin hebdomada (“number seven; group of seven; seven days”), hebdomas (“number seven; seven days; seventh day”), from Ancient Greek ἑβδομάς (hebdomás, “group of seven, especially seven days or seven years”), from ἕβδομος (hébdomos, “seventh”) + -ᾰ́ς (-ắs, suffix forming abstract nouns of number from numerals). The word is cognate with French hebdomadaire, hebdo (“weekly periodical”), hebdomadairement (“weekly”), Portuguese hebdomadário (“weekly periodical”), Spanish hebdomadario (“weekly; weekly periodical; hebdomadary”).
Adapted from the Wiktionary entry hebdomad (CC BY-SA 4.0).