Where does “pěkrъ” come from?

pěkrъ (Proto-Slavic) comes from Proto-Indo-European peh₂ḱ- — to join, to attach; agreement, settlement.

Ancestry of “pěkrъ”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	peh₂ḱ-	to join, to attach; agreement, settlement

pěkrъ — Etymology, Origin & Word History | Etymology Explorer