Where does “миленький” come from?

миленький (Russian) comes from Russian ми́лый, from Old East Slavic милъ, from Proto-Slavic milъ, from Proto-Balto-Slavic meiʔlos, from Proto-Indo-European meyl-.

Ancestry of “миленький”, step by step

Step	Language	Word	Meaning
1	Russian	ми́лый	dear, sweet; sweetheart; dear; cute
2	Old East Slavic	милъ	dear, sweet
3	Proto-Slavic	milъ	dear, nice, gentle, mild, soft, pleasant, polite
4	Proto-Balto-Slavic	meiʔlos	—
5	Proto-Indo-European	meyl-	—

Every word from Proto-Indo-European meyl- →