What is the origin/etymology of phrase Семь пятниц на неделе (literally, seven Fridays in a week)? I am not interested in the meaning of it (I know what it means), but rather where it came from.
I have seen some references to Friday historically being a day off, market day, etc., that is when people could do something beyond/outside their normal day-to-day work, so I can imagine the phrase's origin being linked to it: every day something new. However I'd like to get a more definitive answer.
Snegiryov in Русские в своих пословицах suggests that Friday was a settlement day in Slavic culture and a traditional due date for debts, bonds, obligations etc. It was common to hear: "this will be done (or paid, or settled) by the next Friday".
An irresponsible person would be inclined to shift the due date "just for one day" over and over again so that this constantly drifting due date covers all the weekdays.
Hence, "seven Fridays in a week" means that a person cannot hold to his time estimations.
Maksimov in Крылатые слова offers (and criticizes) another etymology: allegedly, of several dozens of churches standing once upon a time by the Kremlin wall, there were seven churches dedicated to St. Paraskevi of Iconium, glorified by the Russian Orthodox Church as "St. Paraskevi the Friday" (св. Параскева Пятница). However, there no records survived of those churches, neither any of those are extant.
