[ursusmaritimus]

There is an old Slavic word "vtorý" for "second" (not sure about spelling, but it is documented for example in old church Slavonic). Russian still uses "vtoroj" for "second". Several other Slavic languages have a word for Tuesday based on this root, even though their usual word for "second" follows a systematic derivation based on "dva" (two). Examples includes Czech and Slovak ("úterý" for Tuesday in both) and Polish ("wtorek").

[Void_]

You’d think old Church Slavonic to be an obscure language, but in my local church (in eastern Slovakia) you can attend a liturgy in this language twice a week.

[ajuc]

Polish uses both "drugi" and "wtóry" for second (wtóry sounds old style, but most people understand it).

[seba_dos1]

It's also still retained in words that mean "repeat(ed)" - powtórzyć, powtórny.