Where does “ядро” come from?

ядро (Kazakh) comes from Russian ядро́, from Proto-Slavic ędro, from Proto-Indo-European h₁en-d(ʰ)r-óm, from Proto-Indo-European h₁én — in.

ядро (Kazakh): core; nucleus

Definitions

Step	Language	Word	Meaning
1	Russian	ядро́	—
2	Proto-Slavic	ędro	kernel, core
3	Proto-Indo-European	h₁en-d(ʰ)r-óm	—
4	Proto-Indo-European	h₁én	in

ядро — Etymology, Origin & Word History | Etymology Explorer