hebdomad

Hebdomad is a historical English term for a seven-day period, essentially a week. It appears mainly in scholarly, antiquarian, or religious writing and is uncommon in contemporary everyday language. The word derives from the Greek hebdomas (seven) and hebdomos (seven days), passing into Latin and French before entering English.

As a noun, hebdomad denotes the interval of seven days. As an adjective, hebdomadal means weekly; as a noun, hebdomadary can refer to a person assigned to weekly duties, especially in ecclesiastical or monastic contexts. The usage is largely literary or institutional rather than common today.

In historical or liturgical discussion, the hebdomad can be described as the seven-day cycle that underpins the concept of a week, before the modern terminology became standard. Some writers also employ hebdomadal forms to emphasize the regular recurrence of a duty or ritual within a seven-day frame.

Because hebdomad is archaic or specialist, contemporary glossaries typically note it as an infrequent or historical term; the common word for the same concept is week. Related terms include hebdomadal and hebdomadary.