Where does “пѣсъкъ” come from?

пѣсъкъ (Old Church Slavonic) comes from Proto-Slavic pěsъkъ, from Proto-Indo-European pē(n)s-u-ko-.

пѣсъкъ (Old Church Slavonic): sand

Definitions

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

пѣсъкъ — Etymology, Origin & Word History | Etymology Explorer