Where does “пе́сак” come from?

пе́сак (Serbo-Croatian) comes from Proto-Slavic pěsъkъ, from Proto-Indo-European pē(n)s-u-ko-.

Ancestry of “пе́сак”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	pěsъkъ	sand
2	Proto-Indo-European	pē(n)s-u-ko-	—

пе́сак — Etymology, Origin & Word History | Etymology Explorer