Where does “pět” come from?

pět (Czech) comes from Old Czech [[pieti]], [[pěti]], from Proto-Slavic pěti, from Proto-Indo-European poiH-.

pět (Czech): five; to sing

Definitions

Step	Language	Word	Meaning
1	Old Czech	[[pieti]], [[pěti]]	—
2	Proto-Slavic	pěti	to sing
3	Proto-Indo-European	poiH-	—

pět — Etymology, Origin & Word History | Etymology Explorer