I do not what you are refering to, but polish names are easy to "match" when you know them (not like Tuesday and Thursday that I still mix after 20 years of learning)
Monday- poniedziałek- the day "po" niedzieli"
Tuesday - wtorek - wtóry (old second)
Wednesday- środa - środek tygodnia- middle of the week
Thursday - czwartek - czwarty dzień- fourth day
Friday- piątek- piąty dzień - fifth day
Saturday- sobota- sabbath
You may know this already, or not care, but some english days of the week are named after our old gods before christianity was introduced.
Tuesday - tiu's day Wednesday - Woden's day Thursday - Thor's day Friday - Freya's day
Then Saturday, Sunday and Monday are named after Saturn, the Sun and the Moon, as you can probably guess.
If it's an consolation, I'm English and I still have to think for a second when it comes to Tuesday and Thursday, probably because I have Dyslexia.
Full declension at https://en.wiktionary.org/wiki/tydzie%C5%84 . The "ń" is required in the link for it to work :-).
Which leads to the questions: given that "dzień" is (usually) day, what does the prefix "ty" imply here?- it doesn't look much like any form of "siedem" And, where do the forms in "godni..." come from?
It says that it used to mean 'ten sam dzień' (the same day), like another Monday 7 days after Monday. "tygo" seems to be an old version of "tego", the Genitive version.