ferial pert. to a weekday XIV; †pert. to a holy day XV. — (O)F. férial, or its source medL. fēriālis, f. fēriæ holiday (cf. FAIR2). In ecclL. fēria (whence feria, in vernacular use from XIX) is used with an ordinal numeral, to designate a particular weekday (e.g. secunda fēria Monday, etc.), and hence in liturgical use for a weekday as dist. from a Sunday or other feast day. The use appears to have arisen from the naming of the days of the octave of Easter feria prima, secunda (etc.), ‘first, second (etc.) holy or festival day’; the designation was transferred thence to the days of ordinary weeks.

ferial. The word comes from the Lat. feria, ‘feast day’, but has by etymological perversity come to mean an ordinary day, as distinguished from a feast. Hence the application of ‘ferial use’ to liturgy and mus.