Where does “szczur” come from?

szczur (Polish) comes from Proto-Slavic ščurъ, from Proto-Indo-European skewh₂- — to lash, to swing, to buzz.

szczur (Polish): rat

Definitions

Step	Language	Word	Meaning
1	Proto-Slavic	ščurъ	playful, mischievous, perky; void, idle; type of...
2	Proto-Indo-European	skewh₂-	to lash, to swing, to buzz

szczur — Etymology, Origin & Word History | Etymology Explorer