Where does “ředidlo” come from?

ředidlo (Czech) comes from Czech ředit, from Old Czech řěditi, from Slovak riedky, from Proto-Slavic rědъkъ, from Proto-Balto-Slavic redʔ-.

ředidlo (Czech): thinner

Definitions

Step	Language	Word	Meaning
1	Czech	ředit	to dilute
2	Old Czech	řěditi	—
3	Slovak	riedky	rare
4	Proto-Slavic	rědъkъ	sparse, rare
5	Proto-Balto-Slavic	redʔ-	—

ředidlo — Etymology, Origin & Word History | Etymology Explorer