hebdomad

Etymology

Comes from Late Latin hebdomada (“number seven; group of seven; seven days”) and hebdomas (“number seven; seven days; seventh day”), which go back to Ancient Greek ἑβδομάς (hebdomás, “group of seven, especially seven days or seven years”), from ἕβδομος (hébdomos, “seventh”) plus -ᾰ́ς (-ắs, suffix forming abstract nouns of number from numerals). It is cognate with French hebdomadaire, hebdo (“weekly periodical”), hebdomadairement (“weekly”), Portuguese hebdomadário (“weekly periodical”), and Spanish hebdomadario (“weekly; weekly periodical; hebdomadary”).