Where does “pleses” come from?

pleses (Old French) comes from Latin placeo, from Proto-Indo-European plā-k- — wide and flat.

Ancestry of “pleses”, step by step

Step	Language	Word	Meaning
1	Latin	placeo	I am pleasing or agreeable to; I please; I am...
2	Proto-Indo-European	plā-k-	wide and flat

pleses — Etymology, Origin & Word History | Etymology Explorer