Lit. 'weekday one'. In this period, days of the work were referred to in Latin, and were named, as today, after pagan gods or the moon and sun. Church writers, sensitive to these pagan references, sometimes preferred to use a neutral nomenclature, which was to number the days of the week. Thus there was feria una for day one, i.e. Sunday, feria secunda for day two, i.e. Monday, and so through the week. -
Cf. Noon
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.