The Collaborative International Dictionary of English v.0.48:

Feria \Fe"ri*a\, n.; pl. Feri[ae]. (Eccl.)
   A week day, esp. a day which is neither a festival nor a
   fast. --Shipley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

feria
    n 1: a weekday on which no festival or holiday is celebrated;
         "in the middle ages feria was used with a prefixed ordinal
         number to designate the day of the week, so `secunda feria'
         meant Monday, but Sunday and Saturday were always called by
         their names, Dominicus and Sabbatum, and so feria came to
         mean an ordinary weekday"
    2: (in Spanish speaking regions) a local festival or fair,
       usually in honor of some patron saint