ETYMOLOGY
probably from the time when Friday was a day of abstinence
EXAMPLE
“…The Fox on a time came to visit the Gray, partly for kindred, chiefly for craft, and finding the hole empty of all other company, saving only one Badger enquiring the cause of his solitariness: he described the sudden death of his dam and sire with the rest of his consorts. The Fox made a Friday face, counterfeiting sorrow: but concluding that death’s stroke was inevitable persuaded him to seek some fit mate wherewith to match.…”
From: Greene’s, Groat’s-Worth of Witte, bought with a million of repentance
Robert Greene, 1592
Lexicophilia 