The word „Rzeczypospolita” consists of two parts.
– The word „rzecz” can be translated as „thing”
– The word „pospolita” as „common”
However, the context should be remembered. The word „rzecz” has the meaning of something valuable. Something that has great value in itself. And at the same time has no price. Because it belongs to everyone.
The word „rzecz” can be replaced with the word „wartość/wartościowy” which means „value/valuable”.

The word „commonwealth” seems to be the closest word. It reflects the true meaning hidden behind a single word.
That’s all that would take volumes of books to describe. Locked in a single word.

Commonwealth
or
a full sentence
Commonwealth of Poland