Etymology and different signification of the word Feria. The word is derived probably from the Latin feriari (to rest). Among the Romans, the idea of a day of rest and a holy day was intimately united and received the name of feria. But it was amongst the Hebrews that the day set apart for the worship of God received the most distinctive character as day of rest (Heortology, p. 2). Hence the early Christians called the days of the week feriae.
Why did the Church adopt the word feriae? She wished to mark the day of the week and not to name them by their pagan name (e.g., dies lunae) nor by their Jewish names (e.g., prima sabbati), which should be a sort of recognition of the dead and dying synagogue. Hence she adopted the word feria, to denote the Christian rest in the Lord, the Christian peace and the abstinence from all sin, and that each and every day should be consecrated to God. The Christian use of the word is found in Origen (185-254) and was fully established in the time of Tertullian.
In the time of Amalare (circa 830) the ferial office had taken a well-defined form, Matins having twelve psalms and six antiphons. In Lauds of every feria were recited the psalms, Miserere; Deus, Deus meus; Deus misereatur nostri; a canticle drawn from a prophet and varying each day of the week (e.g., Confitebor, Isaias xii., for Monday’s Lauds; Ego dixi, Isaias xxxviii., for Tuesday’s Lauds, etc., and the two psalms Laudate (148, 150) and the Cantate, psalm 149). In the small hours the Sunday psalms without antiphons were recited. Vespers had daily, fixed psalms. At each hour the Kyrie Eleison and ferial prayers were said on bended knees and the hours terminated—as do the hours of Holy Week still—with Pater Noster and Miserere.
Ferias are divided into three classes, major ferias, privileged ferias and non-privileged. Ash Wednesday and the three last days of Holy Week are the major ferias which are privileged and exclude all feasts (vide Tit. II., sec. 2). Non-privileged feriae are the feriae of Lent and Advent, Quarter Tense or Ember days and Rogation Monday. They take precedence of simple feasts only.
In the ferial office nine psalms are said, and not twelve, as in the old order of the Breviary. The psalms found arranged in the new Breviary for three nocturns are to be said with nine antiphons up to the versicle of third nocturn—the versicle of the first and second being omitted (Tit. I., sec. 7). Hence the psalms are to be said straight through (sine interuptione) omitting in the first two nocturns, the versicle and response, Pater Noster, absolutions and all pertaining to the lessons. This simplifies things and makes the ferial office shorter than the office of feasts.