feria = fair

Feria Latin for free day.

Learn how it became “fair” in English.

“A day on which the people, especially the slaves, were not obliged to work and on which there were no court sessions.

“In ancient Roman times the feriae publicae, legal holidays, were stativae, recurring regularly (e.g., the Saturnalia); conceptivae, i.e., movable; or imperativae, i.e., appointed for special occasions.

“When Christianity spread, the feriae were ordered for religious rest, to celebrate the feasts instituted for worship by the Church.

“The faithful were obliged on those days to attend Mass in their parish church; such assemblies gradually led to mercantile enterprise, partly from necessity and partly for the sake of convenience.

“This custom in time introduced those market gatherings which … the English called fairs [see the similarity to feria?].”
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https://www.newadvent.org/cathen/06043a.htm